Add start-app.py

Simple script to run twistd from python. Py2app doesn't like non python entry.

I'm having a bit of an issue getting libpython2.7.dylib. On my system, I use pyenv, and with it, I've lost/forgotten a bit about path management.

Another approach I will try is using the brew installed version of python and then somehow get setuptools working there. (I'm relatively sure I'm over complicating things here).