Implement JavaScript UI for attachments

This one is a bit of a doozy. A summary of the changes:

- Session has grown storage for attachments which have been uploaded but
  not yet sent.
- The list of attachments on a message is refcounted so that we can
  clean up the temporary files only after it's done with - i.e. after
  copying to Sent and after all of the SMTP attempts are done.
- Abandoned attachments are cleared out on process shutdown.

Future work:
- Add a limit to the maximum number of pending attachments the user can
  have in the session.
- Periodically clean out abandoned attachments?

1 files changed, 2 insertions, 0 deletions

diff --git a/cmd/alps/main.go b/cmd/alps/main.go
index dedd6cb..e519332 100644
--- a/cmd/alps/main.go
+++ b/cmd/alps/main.go
@@ -101,4 +101,6 @@ func main() {
 	e.Logger.Print("Waiting for work queues to finish...")
 	s.Queue.Shutdown()
 	e.Logger.Print("Shut down.")
+
+	s.Close()
 }