Fix teardown of resize handler in content management screen
Fix teardown of resize handler in content management screen

refs #5659 ([comment](https://github.com/TryGhost/Ghost/issues/5659#issuecomment-137114898))
- cleans up resize handler on willDestroy hook of gh-content-view-container

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