Tracker: Miscellaneous cleanup

Move DraggableContainerIcon out of ContainerWindow.cpp into new.
Move CompareLabels to Utilities.cpp

Rename fContainerWindowFlags to fOpenFlags. These are the flags set
by OpenContainerWindow to save and restore state and should not be
confused with the windowFlags that are passed to BWindow. There are
two sets of flags, which I'm calling openFlags and windowFlags.

Rename fUseLayouts to fUsesLayout and useLayouts to useLayout. Put
all the constructor created flags at the top.

"window" variable name is ok, we don't need to say "containerWindow".

Rename Addons to AddOns everywhere with a capital O.
Rename BuildAddOnMenu() to BuildAddOnsMenu() with an s.
Rename AttributeMenu...() methods to AttributesMenu...() with an s.
Rename SetUp...() methods to Setup...() with a lowercase u.

Replace a few instances of fPoseView with PoseView() inline in
BContainerWindow and BDeskWindow.

A few more minor fixes in BDeskWindow.

Replace BPoint(0, 0) with B_ORIGIN in Pose.h

Change-Id: If30803753b63b19e35f14c0f0c4e08111d0d0980
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7240
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>