Added `model.wasChanged` helper
Added `model.wasChanged` helper

refs #10461

- helpful if you need to ask if the model was changed
- Bookshelf does not support this feature yet
- https://github.com/bookshelf/bookshelf/issues/1943

JohnONolan/Ghost,janvt/Ghost,ErisDS/Ghost,TryGhost/Ghost,e10/Ghost,Gargol/Ghost,janvt/Ghost,JohnONolan/Ghost,TryGhost/Ghost,Kikobeats/Ghost,ErisDS/Ghost,ErisDS/Ghost,kevinansfield/Ghost,Kikobeats/Ghost,kevinansfield/Ghost,Gargol/Ghost,JohnONolan/Ghost,e10/Ghost,kevinansfield/Ghost,bitjson/Ghost,TryGhost/Ghost,bitjson/Ghost,Kikobeats/Ghost