Enroll url to signup

Change the enrollments url to signup per suggestion on Friday's call. Does not change any internal code details, just the routing thing.

The diff seems to include content update from april too... my local log doesn't show it but maybe we accidentally pulled master? It doesn't hurt anything though, this just updates static site stuff to match master which we might as well do for consistency. I'm not sure how to strip it out anyway...
I dealt with this when I merged staging into master last Friday to do the production release.  I wasn't sure if I got the merge right, but this stuff is obsolete anyway so we can always fix it up before we go live if it's wrong.