Clean up CaptureCraft a little.

Move the orbit setting code into its own function.
Move the docking code into its own function.

I was expecting to need separate code paths for landed and orbital builds,
but while that turned out to be unnecessary, this is still cleaner.
Disable in-atmosphere on-rails vessel deletion.

Since construction keeps the craft on rails for a few frames, KSP wants to
delete it while we're waiting for the parts to initialize. It turns out
there's a clean way to disable that.

This is the final commit needed to fix #3.