Handle crafts with missing parts.

Pretty much just produce a similar report to what loading a craft with
missing parts in the VAB does.
Avoid a key error with JetFuel.

When JetFuel is not required, there's no slider, so just skip the check
completely. Avoids a whole bunch of errors, actually.
Clear out some apparently dead code.

With a RCS, no need to keep code commented out.
Bring back the craft backup creation.

It seems this is required for proper launching of ships that use launch
clamps.
Merge pull request #37 from taniwha-qf/misc-fixes

Misc fixes