Set User Class on Boot

For most of the Rails boot process, an app running solidus_auth_devise
believes that its user class is whatever is configured in the
config/spree.rb initializer. However, if `solidus_auth_devise` is
installed, that is changed after most things have been configured.

It need not be this way: If we want this gem to set a default, we should
set it really early on, not in one of the last initializers to run (they
also run alphabetically, so `solidus_auth_devise` initializers run quite
late.

Author: mamhoff

lib/spree/auth/engine.rb

@@ -13,16 +13,14 @@ class Engine < Rails::Engine
       isolate_namespace Spree
       engine_name 'solidus_auth'
 
+      Spree.user_class = "Spree::User"
+
       initializer "spree.auth.environment", before: :load_config_initializers do |_app|
         require 'spree/auth_configuration'
 
         Spree::Auth::Config = Spree::AuthConfiguration.new
       end
 
-      initializer "solidus_auth_devise.set_user_class", after: :load_config_initializers do
-        Spree.user_class = "Spree::User"
-      end
-
       config.to_prepare do
         Spree::Auth::Engine.prepare_backend if SolidusSupport.backend_available?
         Spree::Auth::Engine.prepare_frontend if SolidusSupport.frontend_available?