Mob implementation

[skykanin]

To start with we will want some basic mobs. It's probably sufficient to start with two kinds of mobs. One melee type and one range type mob. These mobs will need game logic to attack the player and some spawn logic so that the mobs spawn in reasonable numbers and inside the boundaries of the room.

• Implement basic mob types
• Implement game logic to target and attack player
• Implement spawn logic