Added Mob Harness item (tested just in single player atm).
Mob Harness: Small clean-up/fix to entity mounting.
Mob Harness: Add the forgotten case of allowing the user to mount mobs.
Ender Furnace: Add lots of foundation code for the container, te and GUI.

The GUI can actually be opened already, although it doesn't have a texture yet.
Ender Furnace: More foundation/GUI code. Now actually smelts stuff already!

All progress bar and particle stuff and texture changes missing still.
Ender Arrow attack: Allow the random teleportation for EntityLivingBase.
Unmount the entity riding a player, when the player logs out.
Mob Harness: Add a separate active state icon. Use UUIDs for all entities.

Also some fixes and clean-up.
Ender Arrow: Adjust the spawn position once again, to clear mounted mobs.

We also check that the to-be adjusted position is air, otherwise it would
allow teleporting through one block thick walls.
Change the recipes for Ender Arrow, Ender Bow and Ender Lasso. Still temporary.
Add some buttons for the Ender Furnace GUI texture. Not used yet.
Release 0.2.0: (Disabled Ender Furnace, since the logic is incomplete.)