lazyset: rename the class to filteredset All smartsets try to be lazy. The purpose of this class is to apply a filter on another set. So we rename the class (and all its occurences) to `filteredset`.

lazyset: add order awareness to the class Just a bit of extra code makes the lazyset aware of order. This renders orderedlazyset useless. At some point, the `subset` will become responsible for this ordering logic. But we are not there yet because the various objects used as subsets are not good enough.

lazyset: remove min/max This is now handled by abstractsmartset.