Pushable Tile Entities

Added #pushable_chests:stickable block tag, in preparation for honey blocks in the upcoming 1.15 update. Until 1.15 releases, slime blocks are the only entry in this tag. Blocks in this tag will act like slime blocks. They stick to themselves, but they don't stick to other blocks in the tag. This essentially means you can add colored slime blocks if you wanted to.