Remove duplicate code, cleanup when possible

* Settings menu moved to BaseActivity
* Moved strings around where necessary
* Adapted tests
* Various little refactorings

As you can see, the XML Formatter actually **removed** the spaces before the > and /> in the opening tags. From what I can tell, this only happens in the `res/menu/` directory and not for the layouts. What do?


[Testrun](https://jenkins.catrob.at/view/Catroid/job/Catroid-Multi-Job-Custom-Branch/554/)