Update admin users view with totals and expanded sorting options

#### Stories ####
- https://www.pivotaltracker.com/story/show/70293314
- https://www.pivotaltracker.com/story/show/70293156

#### Notes ####
- add totals to admin users view: total # of users, total # of measures, total # of patients
- add select for modifying users view sorting: approval status, email address, measure count, patient count