New Solo Missions

This adds a set of new Solo Missions (with more coming soon). Try out various cars and lorries, and different types of weapons, on different types of combat map. Successful completion also wins weapons, vehicles and DW$ for your gang.

These also serve as quick-play missions for new players who just want to try the game out a bit, without waiting for scheduled town combats/races or for other players to be ready for a multi-player scout.