Add config/environments/environment.rb (for production/staging)

This adds the previously-templated `environment.rb.erb` from the Chef cookbook and has it read from YAML files. When deployed, this file will be coped to `$RAILS_ENV.rb` .

Note that `production.rb` & `staging.rb` are still present; the plan is to remove them once we have no instances still relying on them.
is it possible to put all of this in an initializer?