Sync changes from published unit

[sdaitzman]

Spec

• Published unit changes cause units in course to receive the sync icon, just like components

In Scope

• Sync changes to unit in library that have been published to local instance in course

Not in scope

• Bulk sync (should be integrated with that story)

[sdaitzman]

Sync operations that can be composed to write spec for this to result in intended behavior (via @kdmccormick at libraries delivery team sync):

1. Parent level fields
2. Child fields
3. Add missing children
4. Remove stale children
   • (Not all extraneous ones; imported from other library or manually added intended override content should likely not be removed)
5. Reset order of synced children

Some operations like Remove extraneous children will require specific logic to support intended behavior depending on stale/different-library links. We'll need to plan ahead to ensure this logic and expected behavior can be extended for sections/subsections eventually.

[sdaitzman]

Overrides to test against:

• Add children to parent in course from same library as parent
• Sync individual children in course, then sync parent