rename FIREBALL_EFFECT_TYPE_NAME constant to FIREBALL_NAME
override GameObject methods in Projectile struct
refactor GameField.GetObjects() method: add projectiles in result
fix bug with pointer cast
add constants for projectiles
add useSkill action
refactor ProjectileManager.Do() method: unlink from/ link to cells when it's correct
fix bug with projectiles reached destination: not it's assumed as collision occured