Remove orphaned notifications, add scopes param to app create API

app/models/mention.rb

@@ -4,6 +4,8 @@ class Mention < ApplicationRecord
   belongs_to :account, inverse_of: :mentions
   belongs_to :status
 
+  has_one :notification, as: :activity, dependent: :destroy
+
   validates :account, :status, presence: true
   validates :account, uniqueness: { scope: :status }
 end