Replace pageit in users with django Paginator backed implementation

pageit tried to do too many things not related to pagination (mapped method name to count function, held url name for template) and yet didn't do enough for pagination (didn't validate page numbers, didn't assist in determining which page numbers/buttons to render in pagination widget).

This PR replaces pageit in the users view (other views still continue to use pageit for now) with a new implementation built on top of django's Paginator.