Implement user list filter and bulk edits, refs T1068

Summary:
finished with filer, change role, delete

- filter by role
- modify role for multiple users
- delete multiple users

Not done:

- translate confirmation messages
- add new users (waiting on D557)

Test Plan:
- go to [[http://ushahidi.dev/users]] (or whatever your local domain is)
- use the filters menu to select a role, see list change
- select one or more users, change role
- select one or more users, delete
- if no users are selected, delete and change role are disabled

Reviewers: seth, rjmackay

Subscribers: spaudanjo

Maniphest Tasks: T1068

Differential Revision: https://phabricator.ushahidi.com/D573