Hack push notifications into email app.

For this demo, every time an account is configured we create
two push endpoints (new mail and reconnect) and send those, along
with the user's credentials and the IMAP server's address, to the
push/IMAP proxy. We issue a notification for every new mail.

Currently only GMail is supported, as our push server doesn't really
handle Yahoo Mail.

Note: this patch uses the hardcoded address localhost:8081 for the push
proxy.