WheelSlot

# Feature Overview
Kind: Wheel Slot
Extendable: no
JSON based: no
JSON config: yes

"WheelSlot" is a new class/data-compound added in FVTM 3!
It makes the vehicle able to store custom wheel mounting spot
locations and assign parts to it (which are marked as wheel).
The Wheel (Part) afterwards affects the slot in calculating a
a new height/rotation point for the vehicle.

NOTE: If you want to use a vehicle in the LegacySystem
make sure to either define all default 4 slots in the vehicle config
or be sure that the vehicle has parts which supply all 4 via the
Part - Wheel Positions Function. The 4 slot ids for land/water vehicles are:
"left_back_wheel", "right_back_wheel", "right_front_wheel", "left_front_wheel"

It is planned that in the future a more dynamic system will make
use of all wheel slots in a vehicle, making 3, 6, 8 or more wheeled
vehicles a possibility.

Here a list of current fields a wheelslot config object should/can contain:

• x, y, z - the position of the wheel (e.g. can be found out by creating
  a "marker" in FMT in the central spot where the wheel would be mounted)
  
• y_rot - optional, the wheel rotation on the Y axis,
  used for rendering a wheel correctly (left/right sided)
• drive - optional, if this wheel is a drive wheel - aka powerred
• connector - optional (default 0), "connector" size to only allow compatble wheels
  see Part - Wheel Installation handler to see the relation
• radius - quick way to add a radius value for this wheelslot, if you e.g. set it
  to 8, it will internally parse it to min tire 7, max 9 and min wheel 4, if you want exact
  limiting values, use max_radius, min_radius or min_tire_width settings
• width - quick way to add a width value for this wheelslot, if you e.g. set it
  to 3, it will internally parse it to min tire 2, max 4 and min wheel 2, if you want exact
  limiting values, use max_width, min_width or min_tire_width settings
• min_radius - optional, sets the minimal radius allowed for wheel installation
• max_radius - optional, sets the maximal radius allowed for wheel installation
• min_tire_radius - optional, sets the minimal tire radius allowed for installation
• min_width - optional, sets the minimal width allowed for wheel installation
• max_width - optional, sets the maxial width allowed for wheel installation
• min_tire_width - optional, sets the minimal tire width allowed for installation
• steering - optional, if this is to be regarded a wheel for steering the vehicle
• required - optional, if this wheel is required,
• relative - optional, if this wheel should offset it's position along the part's
  installed position (e.g. on vehicles with varying chassis lengths)