Sluice can eat stacks of 1,2 or 3 items depending on available space. Small performance optimization applied. Fixed the issue with placement of ingot into the existing pile of other metal kind.

If player drops down two gravels then these gravels might combine into stack and not be eaten by Sluice. This update fixes this annoying situation.
Another fix belong to weird behavior of ingot placement. Code refactored a bit.