Delete indexed data when leaving a project

[achou11]

Description

Follow-up item based on discussions around #410. Implementing it requires updating the multi-core and sqlite indexers first, and then updating the IndexWriter and MapeoProject.leave() to take advantage of the changes.

Tasks

• Update multi-core-indexer

• Update mapeo-sqlite-indexer

• Add a method to IndexWriter to call the relevant method for each sqlite indexer instance

• Update MapeoProject.leave() implementation to use the new methods. Also have to keep in mind that the order in which they're called is important:

  1. Delete core data (already implemented)
  2. Reset multicore indexer state
  3. Delete data from index tables