Added a tunable "induced drag" number to aircraft. One of the things that

Added a tunable "induced drag" number to aircraft.  One of the things that
isn't well-constrained by the solution process is the drag-vs-aoa curve.
The default value that YASim picked was very steep, and resulted in most
of the jets flying their approaches *way* behind the power curve.  This
changes the default to be more forgiving, and adds an "idrag" tunable
to the configuration file for tweakers.

Also, change the default gear springiness to be less stiff.