Major refactor and redesign

Summary -- Pretty much everything but the physics changed. Character controllers
have been removed and replaced, many older unused assets removed, and everything
else refactored to work with rigidbody controllers.

Added:
 * Rigidbody ground control
 * walking animation
 * Full editor redesign
 * Better animator
Removed:
 * All character controller scripts
 * All character controller swapping code
 * old Free Flight editor
 * Paper plane assets
 * Base ground controller merged into main Free Flight script
 * Keyboard controller now default functionality, removed old script