Backend: When a component is edited, all parent Units must show changes

[bradenmacdonald]

1. When a component is edited via the normal Content Libraries APIs, we need to check if it's part of any units, and if so then update the search index to show that those units now contain unpublished changes.

Note: the units themselves may not have unpublished changes, but they contain unpublished changes. The Learning Core low-level APIs distinguish between these two states, but our search index and UI don't need to distinguish between them.

2. When a component is deleted via the REST API, the "component count" for any units containing that component should be decreased in the search index.