Update requirements to use more modern stuff

* bump reportlab from 2.6 to 3.1.8, a painless drop-in upgrade
* bump requests from 0.14.1 to 2.3.0, making it match the version in use
  on edx-platform. Some small code updates to make this work.
* bump PyPDF2 from 1.19 to 1.23, a transparent upgrade
* remove logging-config dependency, it appeared unused
* remove lockfile dependency, it appeared unused
* remove python-daemon dependency, it appeared unused
* remove simples3 dependency, it appeared unused
* remove wsgiref dependency, it appeared unused
* Trivial import cleanups
* Introduce DEFAULT_ORG variable, so that LONG_ORG configuration no
  longer fails with poorly configured test courses. This also saves
  sites whose certs all issue from one org from having to configure the
  org in every cert.

@jarv or maybe one of @sarina or @db; I think there's nothing controversial here. Most of these requirements were aspirational.
Update to conform to the new Sessions interface in modern versions of requests.