Added CampaignMap and MapLevel classes to the game code.

CampaignMap generates the map every level and passes it down
to the MapLevel class to render and set up player interaction.

Both classes are still a work in progress.
Added a tutorial map to the game. The map is loaded from an XML file and
will be static, except for road denominations.
Game now displays fraction values near each road segment.
The car is back and can drive across roads one at a time when the
player clicks on a valid road.