Battle of Britain remake of PSS game CodeSVN

Added changing weather.

Preparing to add weather.

Minor changes.

Added probability to pilotsDead method.
Changed pace of refreshing gamescreen.

Better loading of image files.

Experience is not added instantly now. It is stored as "gained experience" which will be added at the end of the day. So results of pilots' learning in combat are not in effect until the next day. This will prevent fluctuations of experience during the day (eventually lowered at the end of the day by recruits coming to squadrons as replacements) which would be unrealistic.
Added new conditions to painting squadrons on the map: squadrons with status = 7 (mission completed) are painted. German squadrons which are not spotted by radar or observers on ground - are not painted.

Adding experience after air combat.

Landing menu now warns when airfield is closed or its runway damaged. Squadron can't choose to land on closed airfield.

Refueling and rearming time now affected by amount of damage inflicted to airfield.

Added hidden German airfields at the eastern edge of the map - these will be their starting positions in regular game. German squadrons can land now and be refueled and rearmed.