Move app to subfolder to help with dockerfile later

In order to dockerize Steam Dissector, it's easier if the app is inside a subfolder. With a subfolder we can create a Dockerfile in the root directory and add app codes to the container with a single ADD command. I believe this is also a common pythonic pattern, but dunno.

Updated readme and Procfile and added __init__.py and __main__.py files for running with gunicorn and via the command line.