Move messages and message settings into a sub app, refs T347

Summary:
- Moving messages listing into a sub app
- Move message list code into message/list and add MessageListController
- Move data provider config into messages app
- Rename 'DataProvider' views to 'Provider' views. And config -> settings

Test Plan: Check that messages and message settings UI works as expected

Reviewers: eyedol, shadowhand

Reviewed By: shadowhand

Maniphest Tasks: T347

Differential Revision: https://phabricator.ushahidi.com/D193