Part Connector Installation Handler

# Installation Handler Overview
Name: Connector Installation Handler
Function: adds the ability to modify the vehicle's connectors via parts
From FVTM: yes

This Installation handler allows you to install a part as either
"front_connector" or "rear_connector", the aim is to be able
to modify the vehicle's front and rear connector points.

The Front and Rear one are both used for rail vehicles.
The Rear one is mainly used for adding a "trailer hitch" to land vehicles.

Example config:

{
    "__comment": "Part JSON file.",
    "Installation":{
    	"Handler": "connector",
        "Removable": true,
        "RearConnector": [ -50, 8, 0 ]
    }
}

Here an overview of the available fields:

• Handler - the id of the wanted handler, it is connector
• Removable - (boolean) optional, if the part can be afterwards removed from the vehicle
• Front - optional, json array with the x/y/z position values of the connector,
  alternatively if you want to support more vehicles with varying connector positions
  make it an json object instead with key/arrays, e.g. see example at Rear
• Rear - optional, json array with the x/y/z position values of the connector,
  alternatively if you want to support more vehicles with varying connector positions
  make it an json object instead with key/arrays, e.g. (example from FVP)

  "Rear": {
      "fvp:t1p": [ -100.5, 2, 0.5 ],
      "fvp:ot1": [ -80.5, 2, 0.5 ] 
  }

• Compatible - optional, same as in Part - Default Installation Handler,
• SlotBased - optional, same as in Part - Default Installation Handler,
• Relative - optional, if the connector position should offset along the part
  installation position (similar to WheelSlot "relative" option/setting)

Note: if not specifying a rear or front connector in the installation handler
config, it will regard it that this part does not add that, this allows for parts
that only add one connector side (e.g. trailer hitch for cars).