Add a toggle key for showing the path markers: CTRL + Hide GUI.

Also changed the modifier key for adding a target point to END, which
is also they key that is used when removing a target point.
Always lock the controls in motion mode.

Leaving them unlocked is pretty much just asking for problems.
Add the ability to move path points.

This is done by "selecting" the point you want to move by being closest
to that one, press CTRL + Multishot menu key to store the index of that
path point, then move to where you want it to be, and press
CTRL + Pause key to create a new point that replaces the one you selected.