Restore original coloring

This set of commits undoes the darkening of the overall color scheme, in favor of the lighter color scheme which brands Linux Mint (the candy green).

It's an architectural set of changes which removes manual color references in the theme files (making it much easier to tweak the theme, or re-color it entirely), the re-shade of menubar and treeview items to restore the light coloring, and re-organization and tweaking of the theme colors to more perfectly match GTK2/3.

The overall effect is below.

NEW:
![New](http://i.imgur.com/fTdzUrS.png)