ensure timestamps include tzinfo

Calling timestamp.utcnow() just results in a datetime object without any tzinfo.  This change explictly includes the UTC tzinfo on the datetime object so it's unambiguous
what the timezone is.
support running integration and performance tests

* Infrastructure for running performance and integration tests
* Basic tests of both types for the MongoDB backend

Uses "make" to simplify the execution of the various commands.  We could probably integrate with manage.py or setup.py or something more sophisticated in the future if necessary.  For now I wanted to KISS.