midi wizard: add checkbox for "add output for this input"

[Owen Williams]

very often, the midi message a button generates is the same as the midi message used to light it up. In the midi mapping wizard we should have a way to quickly try the and see if the button illuminates. The flow would be like:

choose control --> learn --> confirmation screen --> "Try light" button --> return to confirmation screen.

Or we could just automate it:

choose control --> learn --> if button, say "attempting to illuminate button" --> did it work y/n? --> confirmation screen.

The confirmation screen would have a checkbox with "illuminate button".

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7856