Implement color spaces and transforms in the OTIO schema

[reinecke]

#170 and #857 define how color transforms and color space are expressed in OTIO. Those definitions should be used to express color information within a timeline.

Some things that we may chose to communicate:

• The Color Space of a piece of media an editor used when building a timeline
• The color space used for a timeline in an NLE
• CDL transforms attached to clips in an EDL
• Per-clip LUTs applied to an edit