Beginnings of Usage Event Parsing

This PR introduces the idea of parsing compute notification for information that a billing system would be interested in. it uses that information to build an expected model, so that when it gets an exists notification it can build an actual model table which can be used to compare with the expected.

Currently, it can only handle successful creates, resizes, resize-reverts, and deletes. It can also handle receiving notifications after the initial start out of order. It parses the exists notification and builds the exists table, but there is no mechanism for actually validating that yet. PRs in the near future will introduce mechanisms that can handle error cases and receiving even the start notifications out of order.

This PR also introduces unit and integration tests to Stacktach. Unit tests are simple nosetests which can be run with ./run_tests.sh. Integration tests are run through django's manage.py utility. They can be run with ./run_integration_tests.sh.