Fixed various Race file reading issues

Accounted for refresh abilities and tech specs on planets. Accounted for
Winnu's "?" multiplier on flagship. Fixed issue where Yssaril and Saar
were missing an 's' at the end of "XRD Transporters". Fixed a typo in
spellcheck.py
Made UnitManager only set prereqs once

Didn't update a bool properly before, so it was setting the WarSun
prereq on every Update call
Added annotation to Unit class

shots variable: "A value of -1 represents a special values ("?" for the
Winnu flagship)"
Added systems file reader

Added: systems file reader, system & planet file processing tool