Tracking pixel server - flask implementation [MJ-480]

Making Django work without a database looked like it was going to take me longer than it did to learn enough Flask to do the job.

If you haven't used Flask before, the main file (pixel.py) can be run with your interpreter of choice and will act similar to Django's runserver. This will start a server that listens on port 5000. You can pass debug=True to app.run() to enable a Django-like debug page with embedded terminals for running arbitrary code.

Tests are slightly different, but can be run by executing pixel_tests.py.

If this is deemed acceptable, I will update deployment with an appropriate set of server configs.

All tests pass.