Added warning dropdown
Events got loaded twice
Deactivated NSURLCache and remove cachePolicy code

NSURLCache seems to have a problem with Cache-Control="private" headers. Most resources of GitHubs API use this header and the response gets cached longer than the interval given by GitHub (in most cases 60 seconds). This way we lose caching, but its still better than unexpected results.
Added test for TeamAddEvent
Cleanup
Refactoring: Comment saving
Refactoring: Issue object saving