Clean up formation creation and get it working(ish)

Also threw in the beginnings of a "story mode" game mode
fix Json files' formatting
Improve Json path parser
Prevent the game from crashing when there are no bgm files
Fix scene manager registering
Fix bspline path loading from the parser
Fix enemy spawning

Formations only create entities, they don't add them to the world, we
let the system do that
Use inherited system maps