[WIP] Accumulate short presses
This allows to directly enter a specific complex mode without switching between various intermediate modes (e.g. ramping/frozen or level increment) by accumulating fast presses for 400 ms and performing the action only after that time. The downside is that mode changes (next level in fixed mode or ramp freezing) is also delayed. When entering config mode the light does not turn off anymore. This way of switching modes might allow some more optimization of the event handling, but probably not with such minimal differences betweeen both implementations. On the other hand it makes mode transitions much more pleasant to the eye (actual usability to be evaluated).