changed visibility and added toString to
core.problem.vehicle.VehicleTypeKey
modified .addPenaltyVehicles() in core.problem.VehicleRoutingProblem
such that penalty-vehicles can also shadow vehicles that only
distinguish themselves by their working shift
bugfix #96 - modified core.problem.vehicle.InfiniteVehicles according to
changes in core.problem.vehicle.VehicleTypeKey
bugfix #96 - modified core.problem.vehicle.VehicleFleetManagerImpl
according to changes in core.problem.vehicle.VehicleTypeKey