:recycle: refactor systems
:recycle: refactor systems

- introduce commands (thrust / firing)
- add input keys as a singleton
- add a apply function for pairs tuples

Signed-off-by: Chris Camel <f7d69a896c9ea808d2bad017ca5719dd54190169@gmail.com>

ccamel/playground-elm,ccamel/playground-elm,ccamel/playground-elm