Sign in overlay

Added a sign in overlay to the app sign in button click
Sign in overly with login trigger

Now we call the sign in overlay as well as the potential login template
and controller.
Sign in overlay and user states

Fixed the animation issue. Got user sign in with FB and G+ using
firebase simple login and a cool loading animation when moving between
user states. User state 0 is not logged in. State of 1 means in process
of checking sign in. State 2 is sully validated and can sign in.
Updated Sign in user and user states

Better sign in sequence with loading page. Also better user state
management
Completed sign in and user state management

Sign in works for active sessions, new sign in session as well as error
in sign in
Create README.md
Completed user login and lout feature

Abstracted all the user management features into a service.
Merge branch 'Login-feature'