Merge pull request #540 from Sleaker/master

Inventory API & EntityInventories
CommandBlock implementation

Signed-off-by: Walker Crouse <walkercrouse@hotmail.com>
Cleanup.
Signed-off-by: Chris Sanders <zidane@outlook.com>
Added canEquip to VanillaMaterial

No longer use Inventory to control if a material is wearable in a specific inventory slot.
All materials default to not being equipable, now override canEquip.
Fixes Skulls & Pumpkins not being equipable in Helm slot.

Signed-off-by: Nick Minkler <sleaker@gmail.com>