[WIP] Mass Codebase Refactor (with a Focus on Combat Systems)

[yungcomputerchair]

Big ol' codebase cleanup:

• New entity hierarchy to add support for non-mob combatants
• NPC Appearance Data is no longer stored, instead created when needed
• Less magic numbers and more utility structs
• (WIP) Reworked Combat, AI, and Ability systems to be more granular & generalized to support ICombatants and event hooks
• Source and header file (re)organization
• (TODO?) Styling pass