Request: Manual GeoFence Enable / Disable

Is it possible to add the ability to enable/disable the geofence manually from MP?
Maybe add MAV_CMD_DO_FENCE_ENABLE etc to the Do Action dropdown list on the Actions tab.
Also a small red/green "F" in the HUD indicating fence off/on would be handy.

Start by tracing the Do Action dropdown on the Actions tab and the HUD entry point, then inspect how MAV_CMD_DO_FENCE_ENABLE and MAV_CMD_DO_FENCE_DISABLE are handled. Done means manual fence enable/disable actions are available and the HUD shows the current fence state; the issue names no files or tests.

Written by the indexing model from the issue text.