In each Moodle file, there are links in the header comments to GNU site and the GPL licence.

Now that most sites are served by https, i think we should update links to reflect that.

So, i propose that we update all links :

http://www.gnu.org/licenses/ to https://www.gnu.org/licenses/

http://www.gnu.org/copyleft/gpl.html to https://www.gnu.org/licenses/gpl-3.0.html

We could also replace "This file is part of Moodle - http://moodle.org/" by "This file is part of Moodle - https://moodle.org/"