Support adding and removing attributes of error templates

config/locales/de.yml

@@ -600,3 +600,4 @@ de:
     hints:
       signature: "Ein regulärer Ausdruck in Ruby-Syntax und ohne führende und schließende \"/\""
     attributes: "Attribute"
+    add_attribute: "Attribut hinzufügen"

config/locales/en.yml

@@ -621,3 +621,4 @@ en:
     hints:
       signature: "A regular expression in Ruby syntax without leading and trailing \"/\""
     attributes: "Attributes"
+    add_attribute: "Add attribute"

config/routes.rb

@@ -2,7 +2,12 @@ FILENAME_REGEXP = /[\w\.]+/ unless Kernel.const_defined?(:FILENAME_REGEXP)
 
 Rails.application.routes.draw do
   resources :error_template_attributes
-  resources :error_templates
+  resources :error_templates do
+    member do
+      put 'attribute', to: 'error_templates#add_attribute'
+      delete 'attribute', to: 'error_templates#remove_attribute'
+    end
+  end
   resources :file_templates do
     collection do
       get 'by_file_type/:file_type_id', as: :by_file_type, action: :by_file_type