User permissions

This adds the user permissions feature, and relevant table structures.  Note that you till have to manually add permissions in the user_permissions table depending on your user id.

Example usage of the has_permission function is included in home-v.php.

Included is an updated skilljoy.sql file.  I suggest we all start working with the same data - so give some thought as to what units / questions / answers you would like in your presentation.  Feel free to delete and add units as you like - then share/commit a skilljoy.sql file with the relevant data.