Let PhFacebook conform to NSCoding

Thus it may be sent to XPC services and execute Facebook requests in there
Retain decoded objects in initWithCoder:
Let PhAuthenticationToken conform to NSCoding
Make setDelegate: method public
Enable WebView to pose as Safari

Safari seems to play nicer with Facebook in terms of consistently providing an auth token
Let Facebook login web view pose as Safari

See previous commit
Remove Cancel button and header controls

This makes it much easier to control from the client whether login is pending or not
Add WebView category to project
Add self parameter to delegate callback
Make debug messages more readable
Support also "Delete" requests and synchronous requests
Saving auth token to user defaults now decoupled from delegate notification
Move from delegate callback API to completion block based API for requesting access
Ignore user specific files
Add NSError object to response dictionary if Facebook returned an error
Remove -facebook:tokenResult: from PhFacebookDelegate

No longer needed after switching to API with block-based completion on login
Improve error handling and ensure invocation of login completion handler when network is down or server does not respond
Remove obsolete method from header file
Allow for providing request parameters to synchronous requests

Do not need it yet for asynchronous requests. Might implement later.
Ensure that completion block on login is called when login window is closed