Forklift compatible loads 1.2

-Added concrete bags, piles of lumber and a crate, all based on vanilla assets.
-Made some changes to the part structure to allow for different types of pallets and stuff
-Added some rigidifiers on the bottom corners of pallets
-Adjusted stiffness to try and reduce the bounciness of most pallet loads when they hit the ground
-Added triangles on the pallet's floor to help with stacking.