Add support for CDL

[jminor]

There were a couple of attempts at adding CDL support before the ALE adapter moved to its own repo:

• Add ALE adapter round-trip CDL values AcademySoftwareFoundation/OpenTimelineIO#1054
• Write color decision list to ale AcademySoftwareFoundation/OpenTimelineIO#1283

If someone wants to continue that work on this repo, we're happy to accept a pull request.

[shidarin]

What are you looking for? Currently it appears to be pulling CDL data correctly from all the samples I have.

We just need to add writing and tests for it?