Add help accessible by a button press with hand in the air

[rpavlik]

The idea is that if you don't know what to do, you throw your hands up and press a button - this would bring up a display of the controls.

We'd probably have a group with toggled visibility, and a function called something like addHelpNode() so that the device config scripts could also add their own help. This would keep things split up nicely between devices.

cc: @jmvance