Add item to trunk export

[Luke20201]

Additions

• A function to find empty trunk slots, counts the number of slots first via vehiclename, then class then reverts to default
• Export to add item to trunk
• Export to remove items from trunk

Modifications

• Modifies the AddToTrunk function, adding the vehicleName and vehicleClass (purpose is for finding out how many slots there are, maybe there's a better way to do this). There is error handling for where the trunk isn't registered already.

Testing
Tested both exports on qbcore, tested to make sure items still worked when adding/removing etc. No bugs found.

Examples
exports['ps-inventory']:AddToTrunk(plate, false, false, "weapon_pistol", 1, info, false, "asea", 2)
exports['ps-inventory']:AddToTrunk(plate, 1, false, "weapon_pistol", 1, info, false, "asea", 2)
exports['ps-inventory']:RemoveFromTrunk(plate, 1, "weapon_pistol", false)

[xFutte]

While at it, splitting this method into smaller methods for readability would be nice.