Expose label text as accessible value instead of accessible name, and
get accessible name from buddy label as any proper input widget does.
Don't expose label tooltip as accessible description unless it's
different from its text (which isn't the case when displayed text is
truncated). Notify on label text and selection changes.
Switch to `SqueezeLabel` for values in statistics dialog which has
similar layout to information tab of torrent properties dialog.
Split FileTree.{h,cc} and FilterBar.{h,cc} files so that each class
is in its own file.
This breaks translations (some classes got renamed => context changed),
to be fixed by next commit (along with Tx sync).
Mike Gelfand