www/py-django-contrib-comments: Update to 1.6.1

• Update to 1.6.1
• Add LICENSE file
• Switch RUN_DEPENDS to file detection

This allows for an existing installation of py-djangoXY to be
identified, which avoids attempting to install py-django (currently
1.8), which will cause installation conflicts for Ports that depend on
contrib-comments, but DONT support Django 1.8 (eg: Mezzanine) and use
www/djangoXY ports.