switch to threadless router.

- add to requirements
- update httptester
- port push backend and add as new submodule
- update settings and urls
- still need to fix tests
fix the push backend / url to prevent needing a data migration
actual fix to urls and settings to match prod
clean imports
properly set router to threadless when sending messages from celery
Merge pull request #58 from dimagi/threadless-router

switch to threadless router.