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)

Fix sure lib at 1.2.3 because new version is broken.

Docs outline

Fixed conf.py file to work locally with RTD template and on RTD.

Update to XBlock version that installs workbench packages.

Wiring up submissions

* Connects the Tim Composition XBlock to the Submissions API so that you
  can submit a composed response.

Running XBlock Workbench in edx-tim

Sanchez/debug submissions page

* Implement a basic XBlock for composing. Allows the user to enter text
  and see what they entered.
* Dirty shell script to install the XBlock demos into this working tree
  so that we can use the workbench for early prototyping. This should
  not be used any more once we integrate into LMS, obviously.

My first pass at populating the submission API.

Conflicts:
	doc/source/conf.py

Conflicts:
	requirements/test.txt

Docs outline