2.5 - More work on Bone Groups

2.5 - More work on Bone Groups

* Added a new UI Template for the 3-colour picker used to visualise + select the custom colours for a bone group.

* Finished wrapping the colour properties for Bone Groups in RNA. Although changing the colour-set used will change the displayed/cached colours, changing the colours via the colour wells will not change the colour set to 'custom' (as per 2.4x) yet. This needs a nice solution...

* Fixed context-related bugs with the Assign/Remove operators for bone groups. These were using context-iterators for selected posechannels, but that was only defined/valid for the 3d view (but not for the buttons window), hence a failure in that case.