Ctrl-F Toggle Safety Switch should be two separate buttons

[rmackay9]

We've had at least one user crash caused by the user "toggling" the safety switch and losing control of the vehicle when they wanted to enable movement of the servos (e.g. safety switch disabled?).

To make it safer we should replace the toggle with two buttons.

We should also check that the button specifies the target system id of the vehicle selected in the Connect drop-down on the main screen.

Related issue https://github.com/ArduPilot/MissionPlanner/issues/3124

[ROSStargh]

Very approving.

#2987

#3269

I've experienced a crash 2 years ago when toggling safety switch under control-F. Multiple drones were connected to GCS. One was in the air, and the others were on the ground. I was trying to take off another drone.

There was no obvious indicator that shows the state of the safety switch. And the command had effect on every drone on the link. So I had no idea all drones had their safety switch already disabled.

It looks like the cause is that the command was sent to target_system=0.