Add Streaming Responses

[bitbyt3r]

This switches to using generators when rendering Jinja templates with the @render decorator. With that pages can be streamed to the client by setting the response.stream property to True on the exposed pageview function.

For now I'm just enabling this on the Attendee Receipt Discrepancies page until more get tested.

[kitsuta]

Looks great! If this works we can make it a decorator for high-intensity pages.

Also, wow, I forgot I'd made this page limit to 50 rows at once. It still doesn't load with even that... something is definitely up with how we query receipts.