ItemStore - Inventory for DarkRP

1. Fixed an ammo duplication exploit

1. Replaced SetWeaponHoldType with SetHoldType in itemstore_pickup

1. Shipments now properly reduce their stack amount in certain situations

1. Pickup now checks if the player has a direct line of reach to the item

1. Using a shipment when the player already owns the weapon it would normally give now gives them the default clip of the weapon.

1. Players can no longer waste shipments and weapons by trying to use them when they already have the weapon

Fixed a dupe bug

1. Shipments cannot be picked up if they are over the stack limit
2. Added third party license information (there's a small bit of DarkRP code used, this is permitted according to the license of DarkRP so long as it's properly credited)