Add standard colors and orientations

[tomgoddard]

It would be useful for visualization to have tables for user-deposited standard colors per asym_id, and a list of standard viewing orientations.

I would read and use this information in ChimeraX. And I could allow ChimeraX to add the color and orientation IHM tables to existing IHM files.

[benmwebb]

Colors would be easy for us to add for many IMP models, since the RMF file format already includes color information. (RMF actually allows each particle to have an assigned color, but I've only ever seen authors assign colors at the chain level.)