Colors used by Bone Groups are now copied/assigned to Action Groups too when
they're created now. This completes the work started in r.46960 to restore this
functionality from 2.48.
Currently, there is no control over when/whether these colors are copied over
(although it is possible to disable the display of these colors for relevant
animation editors if desired). Originally I was going to make this a more
generic Keying Sets feature, though that turned out to be a bit too complex to
manage.
Other notes:
* Split out the code for copying colors to a common library function
1ced356009