added check to use the default contact_us_url if none defined in branding.yml

added raw to feedback emails

updated comment emailer to allow contact_us_url default

visibility communicating with the right controller action. DMPRoadmap/roadmap#732

visibility_allowed method for Plan. Adequate error handling for visibility action. DMPRoadmap/roadmap#732

UserMailer for when the visibility is successfully saved. DMPRoadmap/roadmap#732