Added hook for additional TileEntityItemStackRenderer calls

This PR allows people to add additional calls in the TEISR for rendering their TESR as an ItemStack. This never really was a BIG issue in versions prior to 1.8, as people could just use an IItemRenderer to render exactly what they wanted. However, it's deprecated now because of the fact that you can almost everything with the new system of rendering that you could do with IIRs. Almost. The big thing was this. Without this PR, the only way to render TESRs as ItemStacks is to extend TEISR, and set the instance in TEISR to your instance. But what happens when two people change the instance? Problem. This is my solution.