privacy: tag/index.php should be restrictable to logged in users

A Moodle which has forcelogin set to no allows non-logged in people (and robots) to see user's full names with associated interests on tag/index.php.

In my opinion (and in the opinion of a large school I work with), this should be restricted to logged in users as a default. A "site policies" option could be added to allow non-logged in users to access the page.

I'd be happy to submit a patch for this, just let me know.