additional performance tweaks

- removed all transparent images and replaced them with argb colors
instead
- added new groupbox to support transparency on windows xp (hopefully)
- label backgrounds now match their parents background color
minor cleanup and perf. changes

- updated theme colors to be more consistent
- added custom panel to apply the same tweaks for double buffering and
transparency as groupboxes
- fixed the naming of tab controls
- updated the themes to support alpha colors
- general cleanup
Merge remote-tracking branch 'upstream/master'