dont let users delete themselves

Summary:
- prevent users from deleting themselves on the backend
- refresh Manage Users view when a delete or bulk delete fails
- update notify.js to return useful promises
Fixes T906

Test Plan:
Try deleting users individually, including yourself.
Try deleting various combinations of other users and yourself in bulk.

Reviewers: rjmackay, vladimir, shadowhand

Reviewed By: shadowhand

Subscribers: srutto

Maniphest Tasks: T906

Differential Revision: https://phabricator.ushahidi.com/D435