Big Resource Update

Cleaned up content types (json) for most external resources.
Added ETags with proper handling to StreamEntry, Stream, and Feed
Made StreamEntries handle conflicting and missing IDs appropriately
Changed following to include date of follow relationship - checking for
follow now means checking for non-null follow date. Unfollow also
returns the original follow date.
Updated Activity to include object and verb
Updated ActivityStreamsObject to include CollabinateObjectId