Add a sleep timer

[Bnyro]

Works fine on mobile devices, however I don't have a TV available to see if ti works.

maybe closes https://github.com/mediathekview/zapp/issues/194

[Bnyro]

Sorry for reopening, I accidentally force pushed my branch back without commiting the squashed changes yet :/

[cemrich]

Inspired by this PR I implemented a spleep time with a slighly different UI.

[Bnyro]

Awesome, I'm curious to check it out soon :)