(Fixed take 3) Separate EQUIPPED and EQUIPPED_FIRST_PERSON Item Render Types

This PR has no param renaming, correct param naming convention, less edits and full backwards compatibility without import spam.

Since many items will have different rendering transformations from the held item to looking at another player holding it, I decided this would be handy to have.

Examples of why this is necessary:

Correct Third Person (before change):
http://i.imgur.com/YWwJvhl.png

Incorrect First Person (before change):
http://i.imgur.com/QWAY6NK.png

With the merge I, along with other modders, would be able to render differently from first to third person.

I've confirmed that this builds successfully and works using my ItemRenderer.