Backhand

New features:
- Added a slot to the inventory where the offhand item can be placed. This is configurable! If experiencing compatibility issues, try
disabling this feature.
- Et Futurum's totem of undying now works in the offhand.
- Added JinRyuu's mods compatibility for rendering an emtpy offhand.
- If using an axe in the mainhand and a log is highlighted, the mainhand action takes precedence. Same for shovels & dirt.
- Updated ingame mod info, rendering an empty offhand is now configurable from the mod menu.

Bug fixes:
- Fixed items not breaking in the offhand.
- Fixed offhand item being moved back into the main inventory on login when empty offhand use is disabled.
- Fixed items moving around in the hotbar when moving an item into the offhand while InventoryTweaks is installed.
- Fixed offhand items vanishing on pickup in survival mode if the player's inventory is full.
- Fixed some items vanishing on offhand use.
- Fixed not being able to attack with an empty offhand
- Fixed being able to break blocks behind an entity being attacked with the offhand.

Visual Fixes:
- Fixed offhand and sometimes even mainhand clipping through blocks when using Optifine.
- Fixed right hand's lighting being disabled.
- First person offhand is now rendered directly after the mainhand renders.
- The offhand item no longer shows up on the first main hotbar slot while in creative mode's survival inventory GUI.
- Fixed inventory GUI darkening when eating or drinking with the offhand.