Prepare page specific bundles for EE versions

Currently `app/assets/` is always taken before `ee/app/assets`, because
it is prepended by sprocket-rails. By creating our own initializer we
can insure that `ee/app/assets` takes precedence.

config/application.rb

@@ -219,13 +219,6 @@ module Gitlab
     config.assets.paths << "#{config.root}/node_modules/xterm/src/"
     config.assets.precompile << "xterm.css"
 
-    # Add EE assets
-    if Gitlab.ee?
-      %w[images javascripts stylesheets].each do |path|
-        config.assets.paths << "#{config.root}/ee/app/assets/#{path}"
-      end
-    end
-
     # Import path for EE specific SCSS entry point
     # In CE it will import a noop file, in EE a functioning file
     # Order is important, so that the ee file takes precedence:
@@ -327,6 +320,20 @@ module Gitlab
       end
     end
 
+    # Add EE assets. They should take precedence over CE. This means if two files exist, e.g.:
+    #
+    # ee/app/assets/stylesheets/example.scss
+    # app/assets/stylesheets/example.scss
+    #
+    # The ee/ version will be preferred.
+    initializer :prefer_ee_assets, after: :append_assets_path do |app|
+      if Gitlab.ee?
+        %w[images javascripts stylesheets].each do |path|
+          app.config.assets.paths.unshift("#{config.root}/ee/app/assets/#{path}")
+        end
+      end
+    end
+
     config.after_initialize do
       # Devise (see initializers/8_devise.rb) already reloads routes if
       # eager loading is enabled, so don't do this twice since it's