Add a VehicleType enum?

[Laykel]

Currently, we have only one vehicle type stored in a file, but we could have others. it would make sense to handle those types in the same way we handle VehicleControllerTypes, which means with an enum.

Example of other config file (for a truck):

<?xml version="1.0" encoding="UTF-8" ?>
<vehicle>
    <length>3.9</length>
    <width>1.2</width>
    <maxSpeed>22.22</maxSpeed>
</vehicle>

This is a feature we hadn't planned, but that could be interesting in the long run.