Refactor: Cycling to a previous or next animation is the application's responsibility

[amclain]

The Engine currently contains functionality for cycling to the previous_animation and next_animation (shown below). However, in the 2020-06-23 meeting we realized these are responsibilities of the application rather than the rendering engine. Therefore, we should move this code out of Engine, leaving the engine with the play_animation function for the application to tell the engine which animation should currently be playing.

https://github.com/ElixirSeattle/xebow/blob/e5589fdec01278b23f043fea198c164ce97eed01/lib/xebow/engine.ex#L31-L45

[doughsay]

This was sorta done, should we close this ticket? Or should we change this ticket to reflect that we're still not happy with the functionality being inside the Keys server?

[amclain]

I think we can close it. The keys server is a different topic.

Resolved in #50.