Battle of Britain remake of PSS game CodeSVN

Removed unused variable.

Bombing sequence: adding experience for bombing, expending ammo (bombs).
Created new variable in Squadron.java: pilotsExperienceBombing - experience in performing bombing mission as opposed to experience in air combat (pilotsExperience).

Bombing sequence: added anti air guns defensive fire.

Bombing sequence: added recognizing of target type - needed to calculate bombing value of squadron (various depending on target).
Squadron.java: added method to calculate bombing value of Luftwaffe bomber squadron.

Added bombing register. Works similar to combat register i.e. remembers which Luftwaffe bomber squadrons are over their mission target and checks if more than one squadron is over given target.

Added applying losses to particular squadrons after resolved air combat.

Calculating expended ammo reworked.

Added fighters vs bombers combat.
Calculating expended ammo needs some fixes.

Modified method of calculating hit probability in fighters' combat - now uses difference between combat value (CV) of attacker and defender. Earlier probability was based on attacker's CV only.

Fighters' combat done. Next are fighters attacking bombers. Applying losses to squadrons will be made at the end of combat (not added yet).