Remove flask-script, move commands to click

click (http://click.pocoo.org/) is used by flask to run its cli args.
In removing flask_script (it's unmaintained), we had to migrate all our
commands to use click. This is a change for the better in my eyes - you
don't need to define the command in several places, and it makes
managing options a bit easier.

View diff with whitespace turned off unless you're a masochist.

run_celery.py

@@ -1,6 +1,10 @@
 #!/usr/bin/env python
 # notify_celery is referenced from manifest_delivery_base.yml, and cannot be removed
+from flask import Flask
+
 from app import notify_celery, create_app
 
-application = create_app('delivery')
+
+application = Flask('delivery')
+create_app(application)
 application.app_context().push()