Add switch(es) for manual pump and on-off or auto-manual

[timlandgraf]

In the current design, you switch the pump on by plugging it into the wall. The device should have an on / off (or automatic / manual) switch, and once we are adding this we could also add buttons for pumping in one or the other direction. This could prove useful in a practical setting. Needs a concept how these switches / buttons behave.