Issue 829 update

This pull requests updates the Recent Activity of PyBossa actions using Redis sets for storing the events.

The actions that are recorded and shown are:
 *  When a Project is created
 * When a Project publishes a new blog post
 * When an Authenticated user contributes to a project
 * When a Project completes a task.
 * When a new User is registered.

Additionally, this pull request has improved the way the DB is created from the Python point of view.