If a timer is scheduled with the timer manager while it is already
scheduled, the new exipry time should override the prev. expiry time
instead of adding a second instance of the same timer function.
Signed-off-by: Matthias Blankertz <matthias@blankertz.org>
Change PlayerApp to new architecture
- depedencies injected via named tuple
- some initial type checking
- move on button press logic to PlayerApp
TODO: Adapt MP3 player
