BitBucket integration

This builds on the excellent contribution of @MufriA in this PR: https://github.com/crashlytics/crashlytics-services/pull/31 to add BitBucket integration with Crashlytics.  Stay tuned for updated screenshots and status as we make progress on integrating this.
This method looks a little bit brittle in its current state.  Specifically, if the split logic doesn't work and the conditional fails, we just return nil and proceed with trying to verify in the enclosing method.  I would recommend taking a look at how we do URL parsing in Jira, which I think is a little bit more durable.