Comparing Timelines

There have been requests of the ability to have a tool or library for diffing OTIO data. This includes:
- When things change on items that are the same
- A way to programmatically specify how to hash an item (for example, by a particular metadata key or by name)
- A way to detect when an item has moved to another location in the hierarchy

No file, test, or entry point is named; start by locating the OTIO data model and any existing comparison-related code. Define the scope around changed matching items, configurable hashing, and hierarchy moves, then demonstrate each comparison result with tests.

Written by the indexing model from the issue text.