added login screen with FaceBook
Rewritten login screen with Accounts and Social frameworks. Created User model
changed the method names to more understandable
source files' restructuring.  placing them into folders and groups
added model data filling from FaceBook and exceptions via warnings for user
added storing user information in NSUserDefaults (class PMPActiveAccountService)
added returning saved user from ActiveAccountService
cleaned LoginScreen from unused stuff
added deleting User Info from NSUserDefaults (Logout). minor fixes in ActiveAccountService
added stubbed feed
merged with scherbakov and logot