Appraise pull requests after a CCLA or ICLA is signed

:curry: :fork_and_knife: 

When a user signs a CLA, let's see if there are any `Curry::UnknownCommitter`s with the same GitHub login. If there are, Supermarket should reevaluate the pull request.

Pivotal Tracker Story: [64775098](https://www.pivotaltracker.com/story/show/64775098)