Disable ActionView partial path prefixing

If you want to render alchemy elements in a Solidus controller
namespace, we need to disable prefixing of controller path to partial
paths, or we get an extra `spree` namespace for the element partial
paths and the elements wont render.

Closes AlchemyCMS/alchemy_cms#1626

lib/alchemy/solidus/alchemy_in_solidus.rb

@@ -12,3 +12,7 @@
     Spree::UserSessionsController.include Alchemy::ControllerActions
   end
 end
+
+# Do not prefix element view partials with `spree` namespace.
+# See https://github.com/AlchemyCMS/alchemy_cms/issues/1626
+ActionView::Base.prefix_partial_path_with_controller_namespace = false