Deprecated things in app

[uglrl]

Android studio keeps complaining about background and onBackground being deprecated. One should use surface/onSurface instead. However, surface/onSurface are already used.

This might lead to the app looking strange, since there is no colour distinction between the background and the containers on it.

[worldofjoni]

This is also already deployed in the beta preview. (Please, i want a good looking Mensa App again 😉 )