Initial commit of update to plugin classes

Added the logic to handle 403 HTTP error and Twitter API error 163 when
source user is not found
Added two tests for issue

Added the test to verify that the JSON parser returns the correct error
code when the Twitter API returns a 403 http error with a 163 API error
code.
Added testCleanUpFollows to try to test the TwitterCrawler encountering
an error when retrieving a relationship follow. This test currently
isn't running correctly against the Twitter API simulator, I believe.