Fixed SocialTodos doc and code inconsistencies

Following changes to SocialTodos docs and code:
- Removed obsolete data validator segments from docs to make instructions simpler.
- Updated backend config instructions to match server behavior.
- Changed the code to use "allUsers" usergroup as docs were already having.

Change-Id: I82ed7fa1bbdbdb8eb8cb7c2bf3ca80670f47bf33
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>