Container free space signal

[Koub]

[Koub] Merged several threads into an older one with the same suggestion.

[Loren Pechtel]

I came looking for this with a different use case: mining platforms. Resources are coming in, if space runs out you only want to keep the best ones. Sitting in orbit you don't collect a lot, but if you're moving you can't drop them until you get someplace. Full, have power: upcycling is effectively free. But such a system has to know when it should throw stuff overboard. A slew of combinators (why can't we count total quantity of all qualities??) or a simple check of free space?