[DB MIGRATION REQ'D] Transition Twitter plugin to API version 1.1
* Rewrite TwitterAPIAccessorOAuth to request and parse JSON instead of XML from version 1.1 of the API
** Add JSONDecoder and APIErrorException classes
* Remove all unauth'ed search calls
* Remove all of ThinkUp's API rate limiting accounting code, since Twitter does this for us
* Use Twitter's per-endpoint rate limits
* Update API call paths (and test data filenames)
* Removed fetchFriendTweetsAndFriends
* Removed all page-based favorites processing (pagination deprecated in 1.1)
** Removed now unused favorite_page fields from instances_twitter table
* Added TwitterAPIEndpoint class and tests
* Initialize per-endpoint rate limits
** Build throttling into crawler apiRequest function: check API endpoint call balance against max percentage use ceiling
* Remove unneeded fields from database