Enforce Privacy by removing top users and footer from front page
Privacy mode added to PyBossa. Closes #483

This commit adds the possibility for a project to "lock" all the user based info
regarding site stats, app stats, top users, and leaderboard.

This feature is a "solution" for cases where the applications have significant issues
regarding privacy issues. In these cases you can protect your contributors by using
this feature. By default is disabled.
Unit tests and lock template.
Add ENFORCE_PRIVACY to Travis testing settings.
Fix minor issue with link to datahub repository
Merge pull request #484 from PyBossa/issue-483-privacy

Issue 483 privacy