pundit: convert favorite groups to pundit.

app/policies/favorite_group_policy.rb

@@ -0,0 +1,21 @@
+class FavoriteGroupPolicy < ApplicationPolicy
+  def show?
+    record.creator_id == user.id || record.is_public
+  end
+
+  def create?
+    user.is_member?
+  end
+
+  def update?
+    record.creator_id == user.id
+  end
+
+  def add_post?
+    update?
+  end
+
+  def permitted_attributes
+    [:name, :post_ids_string, :is_public, :post_ids, post_ids: []]
+  end
+end