[api] Redirect to Orders#show from Checkouts#show

Rather than having two actions that do the same thing, let's just combine all the logic into one.

API users: please use /orders/:num from this point onwards.
Bump to 2.0.11.beta
Bump to Rails 3.2.17 in README
[order importer] Set shipping rate to be the selected shipping rate

Conflicts:
	api/spec/models/spree/order_spec.rb