Add MessageLog for high-level tracking of send status. Minor code cleanup.

MessageLog and MessageLogEntry now track a message status: queued, sending, completed, and error. MessageLogEntry will exist for every recipient (including group members but not the group itself) so we may better track SMTP errors in the future.

The code cleanup was mostly cleaning up areas where tabs and spaces were being mixed. I also simplified the 'tooltip' logic by moving the tooltips themselves into the HTML view.