Fire events from authoring_api to trigger library reindexing

[kdmccormick]

This will make it safe for developers to call the xblock_api and authoring_api without worrying about their libraries' indexes falling out-of-date.

• Add openedx-events for component and container authoring
• Fire those events from the authoring_api function calls
• Consume the events in the content_libraries app and reindex content as appropriate
• As appropriate, move functions from libraries_api down into xblock_api and authoring_api, and/or remove unnecessary libraries_api wrapper functions. Update existing references.

[kdmccormick]

FYI @bradenmacdonald -- as we discussed in Slack

[bradenmacdonald]

Thanks for writing this up @kdmccormick !