devel/notmuch-web: single user web front end using python-cffi

Originally contributed by Brian Sniffen [1]. Quite a few unpublished
fixes from Daniel Kahn Gilmour. We've been running it a few years now
as the "official" archive of the notmuch mailing list. There also a
few fixes from myself and Austin Ray. Finally I converted it to the
new python bindings.

This commit squashes the several years of development history and
moves it under devel, in recognition of the now established role it
plays in the project infrastructure.

[1]: id:87tvyvp4f2.fsf@istari.evenmere.org