Pickup Updated.

The pickup script is now split into 4 parts.

PickupMouse1 and PickupMouse2 control the boxes being picked up by the
mouse in the top and bottom worlds respectively.

PickupKey1 and PickupKey2 control the boxes being picked up by the Keys
F for the top world, and G in the bottom world.

PickupKey1 and PickupMouse1 reference each other to keep updated on
whether the player in the top world is holding something.
Same thing for PickupKey2 and PickupMouse2.

Player1 should have the script PickupKey1 attached.
Player2 should have the script PickupKey2 attached.
Boxes to be picked up in the top world should have PickupMouse1
attached.
Boxes to be picked up in the bottom world should have PickupMouse2
attached.

No variables are required to be updated/changed when attaching these
scripts.

Updated the Prefabs with the needed scripts etc.

Note:
Any physics problems encountered by picking up a box while surrounded by
multiple are due to the method used to pickup the box, i.e. the same
reason the boxes clip into walls.