Resources associations for MutlipleChoiceAnswer and OpenResponseAnswer

specs, routes, models, controllers.

When a student answers questions in an activity, their responses are
saved back to the server so that they can be seen when the student
returns to the activity.

part of [#48276409]
https://www.pivotaltracker.com/story/show/48276409
Module Embeddable : factor-out 'table_name_prefix'
Flagging slow specs so guard is faster
rm references to run_html format
Pulling the partial back into the template

This was partial-ized to deal with the run_html format which is now junked. Pulling it back simplifies the view structure.
Fixing spec for page show
Set up controller to assign @modules
Render Answers partials instead of Embeddables
Editing and updating README
WIP on MultipleChoiceAnswers form partial.
Controller code to use @modules instead of page.embeddables.
AnswerFinder Return Answer-type for Embeddable if exists; else Embeddabl

[#45527597]
https://www.pivotaltracker.com/story/show/45527597
MultipleChoiceAnswer & OpenResponseAnswer delegate prompt to Questions.
Get _lightweight.html.haml rendering for answers.

[#45527597] https://www.pivotaltracker.com/story/show/45527597
MultipleChoiceAnswerController: Rough draft / WIP / Placeholder
House cleaning: switch from rvmrc → ruby-version
Gems:  Pry plugins for debugging.
Clearing out old Saveable code
Remove ActivityReponses, move functions to Run (models, controllers, routes)
Remove ActivityReponses : Fix failing tests, add some new ones.