Bugfix for signup screen
Bugfix for signup screen

caused by issue #326
 - implementing fade in and center on signup form by applying the functionality to a shared view
 - login and signup now both extend the shared view

JohnONolan/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin,TryGhost/Ghost-Admin,acburdine/Ghost-Admin,acburdine/Ghost-Admin,kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,airycanon/Ghost-Admin,dbalders/Ghost-Admin,kevinansfield/Ghost-Admin