Speed optimization

[breznak]

Sometimes, our game runs slow! This is due to:

• graphics (lack of) optimizations
• controllers feel sluggish #26
• too large maps in memory #11

[breznak]

@JohnnyMarek please tell me the details of what you have planned :) (PS, upload it here, even if it does not run yet)

[breznak]

Partially related #60