Battle of Britain remake of PSS game CodeSVN

Made background transparent in images of city, airfield and radar station. Added London to map.

Added positions of all cities, airfields and radar station - based on original PSS game positions with a few alterations to fit best with map

Map resized to 1140x660 to fit original game map, which was divided to 22 fields vertically and 38 fields horizontally. Geographically the map covers the same area so image had to shrink a little vertically. Single field size is unchanged: 30x30 pixels.

Displays positions of cities on map. City class has name, position_x, position_y, damage and status attributes.

Displays positions of airfields and radar stations on map.

Added reading data about airfields and radar stations. Data is stored in files: airfield.txt and radar.txt

Added Radar and City classes.
Added position_x and position_y to Airfield class.

Airfield class: added runway damage and weather
Squadron class: added mission target, home airfield, mission status
Main class: comments for main loop (sequence of actions for squadrons)

Squadrons are moving to their targets - they make one move every few seconds

Added setting target for squadrons (also shows target for selected squadron in upper message window)