Hygiene: Some preliminary clean-up for new licensing messages

* Remove mobile-frontend-footer-license message (no longer used)
* Move logic for creating license link to a separate function
* Add a couple more short license aliases (for Wikinews)
* Rename $licenses var to $commonLicenses (less confusing)
* Add ability to add attributes to license link (will be needed)
* Remove param from getTermsLink() since it is never needed
* Fix some member variable documentation in SkinMinerva.php
* Preliminary work for bug 61835

Change-Id: I2fff51251d1f3e34243c99d5fb6f65f9ad07b995
Merge "Hygiene: Some preliminary clean-up for new licensing messages"