[bug 1047386] Fix aggregated L10N metric dashboard

Django REST framework did not like having to pump out the amount of information that the dashboard originally wanted. We were trying to avoid pagination by setting the limit to a really high number and this was causing the API endpoint to take forever (I left it running for like 15 minutes and it still wasn't done). After some experimentation I landed on making multiple requests to the API to the data in smaller packets. I'm assuming this is a low traffic part of the site and this will be okay.

r?