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).