This commit restores the group colours support for F-Curves and F-Curve Groups
in the DopeSheet and Graph Editors. Currently the relevant settings for groups
are only exposed via RNA, but a followup commit will add support for
automatically setting these colours. By default, DopeSheet and Graph Editors are
set to display these colours if/when they are available.
This functionality used to be in 2.48, and is a useful mechanism for visually
distinguishing between channels for different controls when animating (if group
colours are used on the rigs too).
8e97203f7d