Better feedback when saving

[R3voA3]

Saving of larger files takes quite a few seconds. During that time the user recieves no feedback whether or not the saving is still ongoing. When saving has finished only a small message is shown at the bottom. When the user wants to exit the application one is asked whether one wants to drop all changes.

Suggestions:

• While saving, a progressbar should be shown.
• When the user exits one minute after saving, no prompt is shown, it just closes.
• When the user wants to exit the programm without saving before, a prompt opens: Save, Cancel, Exit without Saving

[bux]

Done in a77a5bf