Add admin sign in spec helper

#268

spec/support/features/session_helpers.rb

@@ -1,5 +1,14 @@
 module Features
   module SessionHelpers
+    def sign_in_to_admin_area(user: FactoryGirl.create(:admin_user))
+      visit admin_login_url
+
+      fill_in 'admin_user[username]', with: user.username
+      fill_in 'admin_user[password]', with: user.password
+
+      click_button 'Log in'
+    end
+
     def sign_in_to_registrar_area(user: FactoryGirl.create(:api_user))
       visit registrar_login_url