Change license to 4.0 on footer

[vthunder]

The footer on all pages currently uses the BY-SA 3.0 license. The legal team has requested that we update it to BY-SA 4.0:

• when clicking on the BY button, it goes to 4.0, not 3.0; and
• the text reads: "Except where otherwise noted, content on this site is licensed under the Creative Commons Attribution 4.0 International license.", with appropriate links out where they are currently interjected.

[vthunder]

We seem to have the license footer in several places:

$ grep -l -R "Except where otherwise" *
docroot/license.rdf/cc/licenserdf/rdf/ns.html
docroot/rdf/ns.html
docroot/wp-content/themes/cc3/footer.php
docroot/wp-content/themes/cc4/footer.php
docroot/wp-content/themes/cc5/footer.php
docroot/wp-content/themes/cc5/page.html
docroot/wp-content/themes/cc6/footer.php
docroot/wp-content/themes/creativecommons.org/page-footer.php
python_env/src/cc.engine/cc/engine/templates/macros_templates/engine.html
python_env/src/license.rdf/cc/licenserdf/rdf/ns.html

[vthunder]

All instances changed with commit 2b799fe (with sub-changes in cc.engine, theme, and license.rdf).