Deskbar: use a virtual directory for the user-configurable menu

* Deskbar now uses ~/config/settings/deskbar/menu_entries for its menu,
falling back to /system/data/deskbar/menu_entries, when the former
doesn't exist. The latter always exists and is a virtual directory
merging the deskbar/menu subdirectories of ~/config/settings/ and
<any installation location>/data/. So, if a package provides a
deskbar menu symlink, it is added automatically when the package is
activated. The user can add own menu items by putting stuff into
~/config/settings/deskbar/menu/, only use their own organization by
symlinking it to menu_entries, or do fun stuff by making menu_entries
a customized virtual directory.
* HaikuImage: No longer create any deskbar menu symlinks in the user's
settings directory. Instead add them to the Haiku package.
* OptionalPackages: At least for the optional packages that do have
hpkgs, no longer create deskbar menu symlinks in the user's settings
directory.
* Move all Deskbar settings files to ~/config/settings/deskbar/ and
drop the "Deskbar_" prefix.

Style fixes including reordering #include's in Deskbar

* Reorder includes according to the Style Guide.
* Whitespace changes, mostly making sure there are 2 newlines
between things and making sure there is 1 newline at the end of
each file.
* Make end of header files all in the style of
#endif\t/* _HEADER_GAURD_H_ */
* The one change that is not purely style is to #include <Path.h>
in DeskbarUtils.h instead of DeskbarUtils.cpp because it is used
to define entry_ref for the AddRefsToDeskbarMenu() prototype.

Filtered flat import of Oliver's svn package management branch

Bring the changes that aren't package management related and the ones
that are but don't take effect as long as they are ignored by the build
system into the master.

Summary of changes:
* Introduce private header <directories.h> with constants for a good
deal of paths that should usually be retrieved via find_directory().
* Replace hard-coded paths by using find_directory() or the
<directories.h> constants (e.g. in drivers and the kernel).
* Add find_directory() constants needed for package management.
* Add __HAIKU_ABI_NAME and B_HAIKU_ABI_NAME macros.
* src/apps/deskbar: BeMenu.* -> DeskbarMenu.*,
DeskBarUtils.* -> DeskbarUtils.*
* Change deskbar menu settings directory from ~/config/be to
~/config/settings/deskbar.
* Other smaller cleanups, changes, and fixes.

Flat commit of all changes from package-management branch in svn

Deskbar: use a virtual directory for the user-configurable menu

* Deskbar now uses ~/config/settings/deskbar/menu_entries for its menu,
falling back to /system/data/deskbar/menu_entries, when the former
doesn't exist. The latter always exists and is a virtual directory
merging the deskbar/menu subdirectories of ~/config/settings/ and
<any installation location>/data/. So, if a package provides a
deskbar menu symlink, it is added automatically when the package is
activated. The user can add own menu items by putting stuff into
~/config/settings/deskbar/menu/, only use their own organization by
symlinking it to menu_entries, or do fun stuff by making menu_entries
a customized virtual directory.
* HaikuImage: No longer create any deskbar menu symlinks in the user's
settings directory. Instead add them to the Haiku package.
* OptionalPackages: At least for the optional packages that do have
hpkgs, no longer create deskbar menu symlinks in the user's settings
directory.
* Move all Deskbar settings files to ~/config/settings/deskbar/ and
drop the "Deskbar_" prefix.

Style fixes including reordering #include's in Deskbar

* Reorder includes according to the Style Guide.
* Whitespace changes, mostly making sure there are 2 newlines
between things and making sure there is 1 newline at the end of
each file.
* Make end of header files all in the style of
#endif\t/* _HEADER_GAURD_H_ */
* The one change that is not purely style is to #include <Path.h>
in DeskbarUtils.h instead of DeskbarUtils.cpp because it is used
to define entry_ref for the AddRefsToDeskbarMenu() prototype.

Filtered flat import of Oliver's svn package management branch

Bring the changes that aren't package management related and the ones
that are but don't take effect as long as they are ignored by the build
system into the master.

Summary of changes:
* Introduce private header <directories.h> with constants for a good
deal of paths that should usually be retrieved via find_directory().
* Replace hard-coded paths by using find_directory() or the
<directories.h> constants (e.g. in drivers and the kernel).
* Add find_directory() constants needed for package management.
* Add __HAIKU_ABI_NAME and B_HAIKU_ABI_NAME macros.
* src/apps/deskbar: BeMenu.* -> DeskbarMenu.*,
DeskBarUtils.* -> DeskbarUtils.*
* Change deskbar menu settings directory from ~/config/be to
~/config/settings/deskbar.
* Other smaller cleanups, changes, and fixes.

Flat commit of all changes from package-management branch in svn