Add problem 37 description (Projectiles Coliision)

We need to implement projectiles collision with the walls.
Get rid of Map::update (it is not used anywhere)
Implement projectiles collisions with the walls

To identify if projectile collides with wall we implement collision
rectangle for projectile and pass map to the
PolarStar::updateProjectiles and to Projectile::update methods.

Common code for getting projectile position was moved to its own method.