Fix notifications

https://gitlab.com/soapbox-pub/soapbox/merge_requests/120/diffs#diff-content-917c7fb80cf426cfae1e7baaa21b3d90ccb2b29c

app/models/notification.rb

@@ -74,6 +74,17 @@ class Notification < ApplicationRecord
     type != :follow_request
   end
 
+  def mark_read!
+    user = account.user
+    is_newer = self.id > (user.last_read_notification || -1)
+
+    if is_newer
+      user.last_read_notification = self.id
+      user.save!
+    else false
+    end
+  end
+
   class << self
     def cache_ids
       select(:id, :updated_at, :activity_type, :activity_id)

app/models/user.rb

@@ -38,6 +38,7 @@
 #  chosen_languages          :string           is an Array
 #  created_by_application_id :bigint(8)
 #  approved                  :boolean          default(TRUE), not null
+#  last_read_notification    :bigint(8)
 #
 
 class User < ApplicationRecord