[DO NOT MERGE] Virtualenv merge and procfile fixins

Splitting out some work I did as a byproduct of getting Socorro working on Heroku:

* merged to one virtualenv (still have the old playdoh vendor-lib, that's fine for now)
* switched Procfile to using gunicorn

I expect this to break some tests and possibly require doc changes, so putting up for discussion more than for merging right now.