Reduce Console Spam When Toggling Formation Speed Limiting

[Raptor959]

Toggling formation speed limiting (pressing F11) on and off will quickly fill the screen with the "Formation Speed Limiting ON/OFF" console message.

I think the simple solution is just make the most recent FSL status message replace the last one, The complex solution is to add a new button to the unit command interface so that it is no longer a global command.