Stop validation error notification stack
Stop validation error notification stack

closes #3383
- Calls closePassive() if a new validation error is thrown to display
only the latest validation error

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