Add confirmation when pressing "Define Home" while cutting

[dwaq]

I'm just getting started so I'm still messing around while cutting to get my Z axis right. On one cut, I had to start over twice because I accidentally hit the "Define Home" button in the middle of the cut which causes the program to lose the current position and offset everything. At the minimum, a confirmation box should be added to this button while Gcode is running, but it probably wouldn't hurt to have always have a confirmation box because there's no undo for this button press.

[BarbourSmith]

That's a great point, the "define home" button should be disabled while the program is running.

It shouldn't be too difficult. I believe there is already a flag for if a program is running. Linking that flag to the button status shouldn't be too difficult. We could also disable the direction arrows.