Make keyboard commands visible

[Quimoniz]

Similar to #16 make actions that occur more visible.

E.g. when the user presses the space key (which might happen inadvertently) make like a whole screen filling pause-symbol appear and let it fade rapidly within less than a second. It helps the user more easily detect what is going on. And might assist the user in proper usage.

(I made the mistake myself, pressing space key, pausing the current song, multiple times already).