1838 - Rails 4 and Spree 2.2

:bomb: 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.

Because we are merging into a previously-unused branch, feel free to merge this once the PR is approved.