Hide and show the SelectAll button appropriately

The Select All button is hidden if all items are selected otherwise it is shown.

This applies for:
* `ScriptFragment`: delete, copy
* `LookFragment`: delete, copy
* `SoundFragment`: delete, copy
* `SpritesListFragment`: delete, copy
* `ProjectsListFragment`: delete

Fix issue: #733 

~~Jenkins testrun: [671](https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/671/)~~
Up-to-date jenkins testrun: [766](https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/766/)