Battle of Britain remake of PSS game CodeSVN

Minor adjustments to squadrons' movement: squadrons can't go off map now and when they reach target they start circling over it instead of getting 0 degrees course

Changed method of drawing map and images to avoid flickering.

Changed a little drawing of city names - to avoid overlapping of names when cities are close to each other (including both parts of London)

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.