Make vehilce leasing costs configurable

[schliesser]

Currently there is no way to modify the leasing costs via settings.

function EconomyManager:getInitialLeasingPrice(price)
    return price * (EconomyManager.DEFAULT_LEASING_DEPOSIT_FACTOR + EconomyManager.PER_DAY_LEASING_FACTOR + EconomyManager.DEFAULT_RUNNING_LEASING_FACTOR)
end

LeasingCosts = VehicleBasePrice * (0,02 + 0,01 + 0,01)