Enable NPN

Next Protocol Negotiation extension. See https://technotes.googlecode.com/git/nextprotoneg.html
This seems to be fixed now

I was getting an error about duplicate client_max_body_size directive.
Refactor notifier cron job creation

This commit moves the notifier cron job creation more into hiera,
because we want to add a second job that runs once a week to send
summary emails.

This commit should not change the behaviour of the existing cronjob.
Add notifier cron job for summary emails

Sends emails early on a Monday morning.
Merge pull request #666 from alphagov/notifier-cron-job-refactor

Notifier cron job refactor
Change notifier job to use new entry point

The notifier now also sends summary emails, so it doesn't make sense
for `npm start` to do a single thing.
Merge pull request #667 from alphagov/rename-notifier-entry-point

Change notifier job to use new entry point
Fix JSON parsing error 

‘upstream_response_time: -‘ isn’t handled.
Merge pull request #668 from alphagov/feature/fix-nginx-json-log

Fix JSON parsing error
Configure unattended upgrades appropriately

Take from GOV.UK puppet. Picked up the ITHC that we didn’t appear to be
installing things in the background that we could do.
Merge pull request #663 from alphagov/feature/npn

Enable NPN
Merge pull request #670 from alphagov/feature/unattended-upgrades

Configure unattended upgrades appropriately
Add celery worker to backend-app-1
Replace celery with path to celery in venv

This should allow starting celery without an active venv
Don't manage celery worker process in development
Refactor app resource class

This creates a new resource class, python_app, which the gunicorn_app
resource now uses.

This means that python_app can be used without implying a web app, e.g.
for a worker daemon.