Provide an easy way to install patchwork for production

From a mailing-list discussion:

I think it should be fairly straightforward to make a docker image with
PostgreSQL, django and patchwork. To feed emails to patchwork, I'd
create a new REST entry point that would accept emails given the proper
credentials. Basically the same code as today but decoupling patchwork
from the host the mailing-list is hosted on. Then, mail delivery to
patchwork could be hooked to anything: local delivery (/etc/aliases and
local(8) as documented today) or a script feeding emails from any source
(eg. fetchmail + procmail).