This fixes two issues:
 - if the course pointed to doesn't exist, GA was added to the iframe twice
 - more importantly, we don't want to count these as separate views anyway--
   we just care about the about page itself.
 - I also added a note about where we would put our segment.io widget if we want it
   later

LMS-2581

edx.org: revises course register button background for all cases (verified, riught column, and bottom of page)

edx.org: adds background to register button's html body element for visual blending in course detail view

updated styling for marketing side register button to accommodate second line of text - and IE-specific styling

If a user is already registered for a course but the course has not started
yet, display a grey button that says "you are registered" and goes nowhere
instead of the blue "access courseware" button, which goes to the LMS course
about page (which 404s).

edx.org - reduces padding on course listing register buttons (all states) and resets box-sizing to border box to make a proper box model for element

edx.org - resolved (in a dirty way) iframed buttons picking up style in IE and added in coming soon style treatment

This reverts commit 2b5e8a49, reversing
changes made to db0549be.