Feature: Support account/inbox specific webhooks (#562)

app/models/webhook.rb

@@ -2,19 +2,20 @@
 #
 # Table name: webhooks
 #
-#  id         :bigint           not null, primary key
-#  urls       :string
-#  created_at :datetime         not null
-#  updated_at :datetime         not null
-#  account_id :integer
-#  inbox_id   :integer
+#  id           :bigint           not null, primary key
+#  url          :string
+#  webhook_type :integer          default("account")
+#  created_at   :datetime         not null
+#  updated_at   :datetime         not null
+#  account_id   :integer
+#  inbox_id     :integer
 #
 
 class Webhook < ApplicationRecord
   belongs_to :account
-  belongs_to :inbox
+  belongs_to :inbox, optional: true
 
   validates :account_id, presence: true
-  validates :inbox_id, presence: true
-  serialize :urls, Array
+
+  enum webhook_type: { account: 0, inbox: 1 }
 end