fix newsletter subscription verification
testing periodic tasks
Add a timezone to celery and rename celery -> app
fix weekly newsletter task name
create model.get_all_newsletter_subscribers
Limit celery to one worker for debug purposes
cosmetics
Bugfixes

* celery error emails to admin
* only send newsletter to verified addresses
add base_url_pretty config var
ignore celerybeat-schedule.db
improve weekly newsletter
Add smtp_server config variable
add new send_email task and update other tasks to use it
improve celery error emails
weekly newsletter improvements
more celery config tweaking