deauthorising after startup when user.json does not exist and unreachable
fix for infinite progress indicator if account store access failed
fix for create repo menu item being enabled when not authorised
several major changes and improvements to reachability handling

- added an api request timer to periodically update user data and avatar
- deauthorising if first api request fails (no local data to load)
- public repo timer is no longer triggered by a successful api request but started independently after starting the api timer
- menu icon is adjusted on startup if unreachable
- refactored variables used during status request (in -pollGithub) to differentiate from actual api request variables
- better http request error handling and debug output (silently ignoring NSURLErrorNotConnectedToInternet failures, but responding to 401 and 403 errors likely to signal access revocation)
- timers are invalidated when unreachable, and changes to status timer interval ignored (user defaults is set, but new value is unused until reachable again)
- status menu icon changes depending on reachable state
- local user data (api request json and user avatar) are removed when deauthorising
changing repo creation window title to match menu item
fix for duplicate alerts when multiple requests from different timers fail due to access revocation
implementing NSURLConnectionDelegate and NSURLConnectionDataDelegate methods for repo creation controller and introducing ability to cancel a request