Support modifying of ModuleFuelTanks volume

[blowfishpro]

Very long term, somewhat limited use cases but potentially useful and probably not too hard to implement.

Only one module would be able to do this of course.

[bfrobin446]

I found a use case. Bluedog Design Bureau has several fuel tanks that use B9 Part Switch to select between tanks of different lengths. When I'm integrating BDB and RealFuels, I'd like to continue using B9 Part Switch to control the model and attachment nodes, but let ModuleFuelTanks manage the resources.

When I try to set the volume using the generic module editing features, the subtype that overrides the volume works as long as I'm in the editor, but loading the craft (trying to launch it, or exiting and re-entering the editor) clobbers any resources that ModuleFuelTanks was managing.

The fix might be as simple as skipping the call to Load() on ModuleFuelTanks if the current volume and tank type match what we're trying to set. I'll try implementing that change and see if it makes a difference.