* src/client/components/client-web-view.vala (ClientWebView): Make
  has_valid_height a GObject property so we can get notified about it
  changing.

* src/client/conversation-viewer/conversation-email.vala
  (ConversationEmail::connect_message_view_signals): Fixed to listen to
  has-valid-height changing rather than the old WK1 load-status property.

* ui/conversation-message.ui: Set body_container orientation to vertical
  so adding the attachments widget works as expected.