Disable ability to edit waypoints when it's too late

[orrblue]

User should not able to edit a waypoint in VR if the drone is already on its way there.
Implementation idea: Only allow editing waypoints when mission is paused.

[exofunctor]

I'm unsure about this. As of right now, moving the two waypoints that define the edge that the drone is currently travelling at (ie. front and back) is disabled. Disabling it for all waypoints doesn't seem necessary.

I like however the idea of only doing it while paused.