Make fuel crossfeed tweakable

[Kasuha]

Many parts allow fuel crossfeeding and every now and then people run into problems that the fuel is not drawn the way they expect not because their build is really bad but because fuel feeding logic - while very clever and effective - is unclear to them.

My suggestion is to add tweakables to parts which currently allow fuel crossfeed:

- on structural parts, allow/deny fuel crossfeed completely

- on fuel tanks, allow/deny radial fuel crossfeed (so the tank doesn't allow radial scan if its fuel contents is disabled)

[HafCoJoe]

Yes that would be awesome. Especially now that the fuel levels can be tweaked in editor.

[SofusRud]

I agree that this would be nice. Up until now I have been inserting a structural panel whenever I have had to control fuel flow on my more complicated spaceplanes.