Fix circular deps in project

[DrJacobHolden]

Fixes ALL circular deps by:

1. Removing index files
2. Removing unused imports
3. Ensuring all type imports use import type
4. Replace almost all instanceof Player and instanceof Npc checks with isPlayer and isNpc respectively (using the type property rather than class instance comparison so we don't need to circularly reference)

I have lost at least 2 years off my life.