Fix incorrect 'modelEvent' references in views

Summary:
Rename `modelEvent` to `modelEvents` in views.

Remove obselete binding to model:change event in Tag/User ListItemViews

Test Plan:
- In manage tag/user view: check that item display is updated after tag/user is edited
- Edit a tag to have the same name as another, try to save. See that validation fails, and tag in the listing isn't updated.

Reviewers: shadowhand

Reviewed By: shadowhand

Differential Revision: https://phabricator.ushahidi.com/D118