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
* Update API call paths (and test data filenames)
* Removed fetchFriendTweetsAndFriends
* Removed all page-based favorites processing (pagination deprecated in 1.1)
* Added TwitterAPIEndpoint class and tests
** Build throttling into crawler apiRequest function; check API endpoint call balance against max percentage use ceiling
Closes #1430
[DB MIGRATION REQ'D] Remove deprecated fields and plugin settings from database
Fix 'Error starting crawler; another crawl is already in progress' on manual update