pin requests to a known version, as we believe there's been an upgrade which is incompatible to our usage

Taking out MySQL-python for now because it requires mysql to be installed, so breaks updates on content folks' envs.

- needed for chemical equation parsing, which is about to appear in capa

Added django-wiki's requirements to requirements.txt, because they weren't being included automatically.

updating dependencies for pystache, networkx, graphviz and removing redundant dependency for django-staticfiles

* need to be in mitx/ to install common/lib/*
* create data dir if it doesn't exit
* add a few more log messages
* Change url for our fork of django-pipeline to stop the hanging checkouts.
  It works either way on my machine, so not sure if this will fix it.