Merge branch 'master' into user_exercise_feedback_backend

# Conflicts:
#	app/views/application/_navigation.html.slim

app/policies/error_template_attribute_policy.rb

@@ -0,0 +1,3 @@
+class ErrorTemplateAttributePolicy < AdminOnlyPolicy
+
+end

app/policies/error_template_policy.rb

@@ -0,0 +1,9 @@
+class ErrorTemplatePolicy < AdminOnlyPolicy
+  def add_attribute?
+    admin?
+  end
+
+  def remove_attribute?
+    admin?
+  end
+end