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