Onto 3 and new ruby requirements.
Fix user session redirect.

This currently redirects people to main app routes rather than Spree
routes.

Fixes #236
bump devise
fixes #238
order and checkout path in spree namespace

namespace login and signed in paths

fixes #239
add already signed in translation for en

fixes #240
Update for bootstrap frontend.
add form
Fix specs.
Let spree_core.gemspec handle ruby version.
Update travis to containers.
only load order for specific actions

according to https://github.com/spree/spree/blob/master/backend/app/controllers/spree/admin/orders_controller.rb#5

fixes #242
bump ruby and cancan is part of core.