Move the "Show Group Colors" toggle from a per-editor option to a single
user preference in the Animation preferences.
The old "Show Group Colors" toggle had to be set per editor, and was on
by default. This meant that disabling group colors would require an action
for every file, for every editor.
### Versioning Warning
Note that Blender's sub-version (a hidden number that's used for managing versioning code between various commits of a single release) hasn't been bumped yet in this commit. This means that the code that sets the default to ON of this new user preference is run every time Blender loads the user preferences. Expect the user preference to act like it wasn't saved -- it /is/ saved, it's just that the saved value is overwritten every time it's loaded. This will be resolved when the patch is committed, as only then I can reliably bump the sub-version.