add axes, categories and subjects to admin panel

app/admin/axes.rb

@@ -0,0 +1,3 @@
+ActiveAdmin.register Axis do
+  permit_params :name
+end

app/admin/categories.rb

@@ -0,0 +1,3 @@
+ActiveAdmin.register Category do
+  permit_params :name
+end

app/admin/subjects.rb

@@ -0,0 +1,3 @@
+ActiveAdmin.register Subject do
+  permit_params :name, :category_id, :axis_id
+end

config/initializers/active_admin.rb

@@ -134,7 +134,7 @@ ActiveAdmin.setup do |config|
   # config.comments_order = 'created_at ASC'
   #
   # You can disable the menu item for the comments index page:
-  # config.comments_menu = false
+  config.comments_menu = false
   #
   # You can customize the comment menu:
   # config.comments_menu = { parent: 'Admin', priority: 1 }