Signin error notifications kept from stacking
Signin error notifications kept from stacking

closes #3375
- Prior to showing error notifications, the signin route now calls
  closePassive().

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