1838 - Rails 4 and Spree 2.2

:bomb: This is ready for review, but PLEASE DO NOT MERGE until we are ready to merge the Spree 2.2 branches (JIRA 1838) for all repos.

Also: all comments of the form "# TODO UPGRADE" are temporary, and must be addressed before merge!

From now on, 2-2-nemo-stable will be our main branch. Not 2-2-stable, which should just be a reflection of 2-2-nemo-stable on the original repo.