Create donkey-admin script to run from CL

[wroscoe]

This attempts to separate the core donkey library and users vehicle configurations.

When a user runs pip install donkeycar the donkey-admin.py script will be added to the PATH. This will then allow the user then run commands like donkey-admin makecar mydonkey to create a folder ~/mydonkey that contains all the config files to run the car.

A command can be added during the pip process like this. http://python-packaging.readthedocs.io/en/latest/command-line-scripts.html