Normal / Radial marks on Navball for node-less adjustments

[The Fog]

Right now we have prograde / retrograde / node markers which is of course essential for any type of maneuvers.

However, especially when making minor adjustment burn to close in on a planet, I've found that most of such burns are normal / radial.

Currently the navball does not indicate those directions, and it is not trivial to find those directions manually in interplanetary-space.

I have to drop a maneuver node whenever I want to make such adjustments, which is very much of a hassle, especially when I've already oriented my map-view focusing on the encounter.

My current workaround is to use MechJeb's Smart ASS to point me in the direction I need, but I think a stock implementation on the navball would be more appropriate.

In short, I think adding normal, anti-normal, radial-in, radial-out marks on the navball in orbit-mode would be very helpful.