Add more logging when moving branches with GitHub API.

Trying to collect more information to diagnose GitHub API failures.
Log full exception (with call stack) when app crashes.
Prevent fatal exception if new branch can't be found.
Pause after creating a new branch in a build repo.

This is an attempted workaround for a crash that occurs when a newly-created branch can't be found. It's possible that the GitHub API needs a little time for a reference created via one API to be visible when queried by a different API.
Fix crash if GitHub API returns no data about changed files.
Add 'Created' as valid Jenkins HTTP response when starting a build.