Refactor ScriptFragment (mainly ActionMode)

One important change here is that once we enter the CAB mode for deleting or copying, not "Delete" or "Copy" will be shown, but "Delete 0 bricks" or "Copy 0 bricks" is shown to further emphasis what this mode does. I got the ok from @RoxaneKoitz for this.

[Testrun](https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/710/)