Use a Gtk.InfoBar for displaying the draft button.
* src/client/conversation-viewer/conversation-message.vala: Add draft
infobar template child, edit_draft signal. Remove unused draft-related
code.
(ConversationMessage::ConversationMessage): Add new is_draft ctor
param, when true show the draft infobar.
(ConversationMessage::on_draft_response): New handler for when the edit
draft button on the infobar is clicked.
* src/client/conversation-viewer/conversation-viewer.vala: Remove
edit_draft signal, make a lame attemppt to work out if a message is a
draft and pass that through to ConversationMessage.
* src/client/application/geary-controller.vala: Hook up on_edit_draft
handler to added conversation messages.
* ui/conversation-message.ui: Added draft infobar.
ea8a9c992c