File loader and dynamic targets

File loader implemented (see bottom of TargetData.txt for format)
All targets loaded into memory at start of GameState. GameState can
choose which targets to use as active targets.
TODO: animated/dynamic rotation not implemented
TODO: make system for choosing which targets are active (call reset
before choosing). Maybe 5 targets are active at a time. When all are
destroyed, 5 more are chosen to be active.