Use an explicit initial default patch state

This will make editing states through the admin UI less error-prone, and
will facilitate parsing patches when relying on a default state, as well as
testing.

Use the explicit default state when parsing mails.

Signed-off-by: Dirk Wallenstein <halsmit@t-online.de>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>