Feature: Add ability to disable auto assignment of conversations (#513)

app/models/inbox.rb

@@ -4,13 +4,14 @@
 #
 # Table name: inboxes
 #
-#  id           :integer          not null, primary key
-#  channel_type :string
-#  name         :string           not null
-#  created_at   :datetime         not null
-#  updated_at   :datetime         not null
-#  account_id   :integer          not null
-#  channel_id   :integer          not null
+#  id                     :integer          not null, primary key
+#  channel_type           :string
+#  enable_auto_assignment :boolean          default(TRUE)
+#  name                   :string           not null
+#  created_at             :datetime         not null
+#  updated_at             :datetime         not null
+#  account_id             :integer          not null
+#  channel_id             :integer          not null
 #
 # Indexes
 #