Change speed action fails on APM when in certain modes

[rubenp02]

Expected Behavior

The Change speed action should not appear while in unsupported flight modes.

Current Behavior

On FBW-A/B, Cruise, and other flight modes that don't support it, the action appears. An error message appears if it's used. Currently, the QML visibility logic checks for the aircraft not currently executing a mission (which also may not make sense for APM, as changing speed during a mission is supported).