Implement color spaces and transforms in the OTIO schema

#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

Read issues #170 and #857 first, since this issue relies on their definitions of color spaces and transforms. Then inspect the OTIO schema entry points to determine how the listed media, timeline, CDL, and LUT information should be represented; done means those color details can be expressed within a timeline.

Written by the indexing model from the issue text.