Tracker: use the Layout API wherever possible.

Sorry this commit is so big, but I couldn't figure out how to do this
incrementally without breaking things.

I wasn't able to just merge Aldeck's branch, as it was a partial refactor
of Tracker and didn't just rewrite the UI creation code to use layouts,
and the changes for PM (e.g. addon loading, virtual directories) made it
very hard to merge (it doesn't even compile after an automerge) so rather
than spending time on that, I decided it'd be better to recreate his work.

Miscellaneous notes:
- This partially cleans up BPoseView & subclasses and BContainerWindow &
subclasses -- none of the subclasses and child views abuse the parent's
state, child views, or layout now.
- BFilePanel and BDeskWindow are not on layouts, because:
* BFilePanel docs in the Be Book instructed developers that wanted to
modify BFilePanel's layout to just use FindView() and then move the
views around. Obviously making it use layouts will break all BeOS
apps that do this, and there are a lot of them (Pe, WonderBrush are
just two examples.) I've added a note to the TODO list for R2 to create
a layout-compatible API for this.
* Some replicants (Workspaces, for example) rely on manipulating
BDeskWindow's drawing state. This is incompatible with layouts, as
at least in the case of Workspaces, it breaks a layouted version
of BDeskWindow entirely.
- I noticed a lot of #ifdef BEOS_VERSION ... gunk in the code. Tracker
probably didn't build on BeOS just before this commit, and now it
won't for sure, so I intend to go through and clean that out in the
near future.

This commit also fixes:
- enhancement #4996 (make Tracker's navigator use vector icons)
- bug #3039 (resizing OpenWithWindow flashes the blue border)
- bug #3889 (OpenWithWindow redraw errors)
- a regression that was a side effect of "dynamic_cast<BDeskWindow*>(this)"
always returning NULL when run in the constructor. I just added a "bool
isDeskWindow" to BContainerWindow's constructor that is only set to true
by BDeskWindow.
- a copy&paste error in VirtualDirectoryPoseView that was passing "uint32
resizeMode" as "uint32 viewMode".

Thanks to Alexandre for his original branch (it was a very useful
reference), Axel (for some miscellaneous advice & encouragement),
Adrien & Humdinger (for user interface review), and Diver (for user
interface review & testing).

Tracker: style fixes to VirtualDirectoryPoseView

Add virtual directory feature to Tracker

Similar to stored queries, files of the virtual directory type behave
like directories -- i.e. they open in a list-mode Tracker window and
show up as an item with submenu in navigation menus. The file itself is
a plain text file in driver settings format. It can have an arbitrary
number of "directory" entries, which specify the paths of (actual)
directories for which the virtual directory provides a merged view. The
view will not show duplicate entries. For non-directory entries the
first one encountered (according to the order the directory paths are
specified in the file) will be shown. A subdirectory entry will again
behave like a virtual directory.

The support in Tracker isn't perfect yet. I'm afraid major refactoring
would be necessary to get it there.

The virtual directory file type uses a differently colored version of
the folder icon. Alternatives welcome.

Tracker: use the Layout API wherever possible.

Sorry this commit is so big, but I couldn't figure out how to do this
incrementally without breaking things.

I wasn't able to just merge Aldeck's branch, as it was a partial refactor
of Tracker and didn't just rewrite the UI creation code to use layouts,
and the changes for PM (e.g. addon loading, virtual directories) made it
very hard to merge (it doesn't even compile after an automerge) so rather
than spending time on that, I decided it'd be better to recreate his work.

Miscellaneous notes:
- This partially cleans up BPoseView & subclasses and BContainerWindow &
subclasses -- none of the subclasses and child views abuse the parent's
state, child views, or layout now.
- BFilePanel and BDeskWindow are not on layouts, because:
* BFilePanel docs in the Be Book instructed developers that wanted to
modify BFilePanel's layout to just use FindView() and then move the
views around. Obviously making it use layouts will break all BeOS
apps that do this, and there are a lot of them (Pe, WonderBrush are
just two examples.) I've added a note to the TODO list for R2 to create
a layout-compatible API for this.
* Some replicants (Workspaces, for example) rely on manipulating
BDeskWindow's drawing state. This is incompatible with layouts, as
at least in the case of Workspaces, it breaks a layouted version
of BDeskWindow entirely.
- I noticed a lot of #ifdef BEOS_VERSION ... gunk in the code. Tracker
probably didn't build on BeOS just before this commit, and now it
won't for sure, so I intend to go through and clean that out in the
near future.

This commit also fixes:
- enhancement #4996 (make Tracker's navigator use vector icons)
- bug #3039 (resizing OpenWithWindow flashes the blue border)
- bug #3889 (OpenWithWindow redraw errors)
- a regression that was a side effect of "dynamic_cast<BDeskWindow*>(this)"
always returning NULL when run in the constructor. I just added a "bool
isDeskWindow" to BContainerWindow's constructor that is only set to true
by BDeskWindow.
- a copy&paste error in VirtualDirectoryPoseView that was passing "uint32
resizeMode" as "uint32 viewMode".

Thanks to Alexandre for his original branch (it was a very useful
reference), Axel (for some miscellaneous advice & encouragement),
Adrien & Humdinger (for user interface review), and Diver (for user
interface review & testing).

Tracker: style fixes to VirtualDirectoryPoseView

Add virtual directory feature to Tracker

Similar to stored queries, files of the virtual directory type behave
like directories -- i.e. they open in a list-mode Tracker window and
show up as an item with submenu in navigation menus. The file itself is
a plain text file in driver settings format. It can have an arbitrary
number of "directory" entries, which specify the paths of (actual)
directories for which the virtual directory provides a merged view. The
view will not show duplicate entries. For non-directory entries the
first one encountered (according to the order the directory paths are
specified in the file) will be shown. A subdirectory entry will again
behave like a virtual directory.

The support in Tracker isn't perfect yet. I'm afraid major refactoring
would be necessary to get it there.

The virtual directory file type uses a differently colored version of
the folder icon. Alternatives welcome.