Small update to debug instrumentation to make less noise.
Fix wrong check for non-null units. Oops.
Refactor mission function signatures to include price variables.

This paves the way for pulling in prices from the config
file in the future.

Also update the unit logic a little (shamelessly pulled from the
VS data/ equivalent). Change the debug calls from debug.info to
debug.debug, also per the VS data/ equivalent
Add working default vegastrike.config -- /finally/ understood the idea.