provide a hook for skipping Wings

this is a small foray into supporting a no-ActiveFedora application. allow a
hook to avoid requiring `ActiveFedora` based classes eagerly during startup.

lib/hyrax/configuration.rb

@@ -367,6 +367,18 @@ def banner_image
       @banner_image ||= 'https://user-images.githubusercontent.com/101482/29949206-ffa60d2c-8e67-11e7-988d-4910b8787d56.jpg'
     end
 
+    ##
+    # @return [Boolean]
+    def disable_wings
+      return @disable_wings unless @disable_wings.nil?
+      ActiveModel::Type::Boolean.new.cast(ENV.fetch('HYRAX_SKIP_WINGS', false))
+    end
+
+    def disable_wings=(val)
+      @disable_wings = val
+    end
+
+
     attr_writer :display_media_download_link
     # @return [Boolean]
     def display_media_download_link?

lib/hyrax/engine.rb

@@ -82,7 +82,7 @@ class Engine < ::Rails::Engine
 
     initializer 'requires' do
       require 'power_converters'
-      require 'wings'
+      require 'wings' unless Hyrax.config.disable_wings
     end
 
     initializer 'routing' do