Added Resource to the Model as a wrapper around the resources with a dirty bit.
Adds test and widgets fixes after the model changes.
EditScene action sets the id of the scene as the modified resource.
Adds ResourceModifiedListener.
Adjusts Save action after the recent changes.
SaveGameTest improvements.
Small fixes after rebase.
Merge pull request #696 from RotaruDan/savingSystem

Saving system improvements