Added update() method for World
Game now uses TanskController to update

Controller stores mouse coordinates. Tank uses those when updating
turret direction.
All entities now has a shape

The default shape is a point located outside the game map (-1, -1).
Implemented basic collision detection logic
The shape now gets rotated and translated upon movement and change of direction
DefaultTank now has a shape of a rectangle
DefaultTank now reacts to collisions by playing a sound
Added an obstacle to the map
The shapes now get drawn
Added ability to remove obstacles from World
Entities now removes themselves upon destroy()
Projectiles now get destroyed
Merged branch Collision to master