Adds gitattributes and removes references to lists.learningu

Adds a ```.gitattributes``` file to:
- force the files we develop in to use Linux LF line endings
- make ````git diff```` work better for us (see the commit message for 6d9d220)

Also commits the line ending changes that git automatically makes as a result of the addition of the ```.gitattributes``` file.

Removes all references to @lists.learningu.org, and replaces them with references to @learningu.org. To do this, also performs a code relicensing.

Partially resolves issue #245. This will not be fully resolved until the ```local_settings.py``` files for each chapter are updated as well.