Move caching initialization to Railtie

Also
- Add reference to config from ActiveModelSerializers.config
- correctly call super in FragmentCacheTest#setup
- rename test rails app from Foo to ActiveModelSerializers::RailsApplication

test/support/rails_app.rb

@@ -1,14 +1,18 @@
-class Foo < Rails::Application
+class ActiveModelSerializers::RailsApplication < Rails::Application
   if Rails::VERSION::MAJOR >= 4
     config.eager_load = false
+
     config.secret_key_base = 'abc123'
-    config.action_controller.perform_caching = true
+
     config.active_support.test_order = :random
+
     config.logger = Logger.new(nil)
+
+    config.action_controller.perform_caching = true
     ActionController::Base.cache_store = :memory_store
   end
 end
-Foo.initialize!
+ActiveModelSerializers::RailsApplication.initialize!
 
 module TestHelper
   Routes = ActionDispatch::Routing::RouteSet.new