More mature error handling around API calls

* Catches SubmissionErrors and sends pass/fail information back to user
  via javascript hidden div.
* Renamed everything from _compose* to just _*
* CSS and js cleanups to make ongoing work less painful (I hope)

@ormsbee and @stephensanchez I figured out my problem and got this working, it's ready to go to master. I haven't done any tests, but I was hoping @stephensanchez could get those in on another commit.