big refactor: CBCFeedManager now manages feeds, and CBCFeed is the abstract base class for local and Medable feeds,
with CBCLocalFeed and CBCMedableFeed derived. CBCLocalFeed uses a SQLLite Core Data persistent store, while
CBCMedableFeed uses an in-memory Core Data "persistent" store. NEXT STEP: Hook up Medable queries to populate
the in-memory store (Medable basically mirrors all changes to the in-memory store). This should be cleaner, faster, and
should avoid those odd Core Data crashes we had been getting.
OK the in-memory Core Data model is now populated with MDPosts from Medable
not 100% working correctly yet, but it's getting close
added code to add the MDPost into the postFromEvent dict for newly-created heart rate events
OK Biogram with refactored Core Data system now works fully, with Medable feeds querying properly, and with the ability to create new Medable posts and delete Medable posts.