Spacers -> individual space height via mouseover

[tewoc]

Next to the essential (t)rack folders (linked to mixer and rack), an updated color sheme and markers, it would be great to have some kind of easy (t)rack orga stuff like "empty space". So that you can just draw some empty space between the tracks and devices by mouseover .... to create individual rack space and track space. Similar to the actual track height option in sequencer.... e.g. mouseover by clicking some arrows and drag them up or down to make big or small space.