Remove capistrano dependency

This is now taken care of by the separate guides_deploy repo
Updates the link to ISO_8601 for the wikipedia in English.
Fixed some footer links
Updated documentation footer contents to match the current website
Update checkout_flow example to match current Spree
Remove implementation details from checkout flow dsl

Those implementation details are not valid anymore due to changes after
split shipments
Use subdirectories (app/controllers/spree and app/models/spree) as preferred place for decorators

h/t JoshuaPaling
Deleting reduntant file so that the right one is served
update ql messages
Moved mapping to its own guide
Update tutorials to use correct message responses
Remove links to guides that are being put on hold. We'll keep the existing content for now.
Update Heroku deployment guide
Add 2.1.0 release notes
Add link for 2.1.0 release notes
Update Getting Started guide with Spree 2.1 + Rails 4
Added details on endpoint.json and registering custom endpoints
Reword Notification vs. Message
Typo fixes
Fix spree version in 2.1.0 release notes.