Embed simple smart answer node in edition

Simple smart answer editions embeds many nodes.
https://www.pivotaltracker.com/story/show/50642999

Includes a workaround to a known issue with Mongoid, `update_attributes` has been overridden to explicitly segregate updates to SimpleSmartAnswers::Node in order to prevent a [conflicting modification error](https://github.com/mongoid/mongoid/issues/1219).