Improved combat math (#70)

[SlappedWithSilence]

Add multi-step damage calculations to Combat that take into account equipment armor and tag resistances.

Armor provides a flat reduction in damage while resistances provide a diminishing-returns model of float reduction.

Various secondary enhancements are included in this branch including:

• Tagging mechanisms for Equipment and Abilities
• Helper methods in the Equipment controller that pre-calculate common values such as tag resistances and armor values
• Major changes to various import structures to resolve persistent circular-import issues
• A bugfix to resolve the Manager-overwrite issue
• A new suite of unit test utilities that enable new types of tests that register and de-register temporary test objects from various managers