This implements a slow mode, for setting a lower maximum azimuth speed in the case of high winds.
A new boolean command is added: slow_mode.
The command is only accepted if the azimuth is (almost) standing still. The new trace slow_mode_used shows whether the slow mode is active.
The control of the slow mode is implemented in the mech.html page.
The maximum azimuth speed in slow mode is hardcoded to be half of the normal maximum azimuth speed.