Merge pull request #83 from MOARdV/master

Update Force Roll string in the MJ menu.
Scale mode.
Actually, I think that's a github twist...
Oneshot option

Closes #84
I think.
Button to turn it off...
Rerender on refocus

That should help. I think.
Config option to permit to disable rays.
Prevent a divide-by-zero in effective throttle computations.

There's not a good reason for a NaN to be a valid answer if there's no thrust.