Django-constant-contact

- Update version of Django.

Added

- Implement work-around for Constant Contact known issue. When
triggered, it causes the Advanced Editor to display nothing.

Changed

- Upgrade version of premailer used.

Changed

- Upgrade pip and setuptools in .travis.yml. django-bulletin
depends on django-minify, which depends on other
packages which need the upgraded setuptools.

Added

- Email content is now html-minified before sending to Constant Contact.

Changed

- Don't allow Django 1.9rcx to be installed.

Changed