Add a new enum for movement type

[CameronJung]

Currently, weather a unit can move on a type of terrain has been determined by the unit type. The new ranged unit will share the terrain capabilities of another unit; therefore a new movement type enum will be added to Universal Constants. The rest of the code concerning terrain and movement will be refactored to check this new property instead of the unit type.

• [x] Add enum to universal constants
• [x] Add and set a movement type member to each unit currently in the game
• [x] change code to check the movement type property instead of the unit type when it comes to terrain crossing
• [x] Play through entire game twice to ensure there are no issues with the refactor

[CameronJung]

The definition of the movement type will be as follows:

0. Legs
1. Rotary Wings
2. Treads
3. Wheels