Add list of recommended families for setting the 'default' option in RMG

In conjunction with commit  https://github.com/connie/RMG-Py/commit/e5507408cd36bb7fcfeb09463d2f5d140f8fdfb7 in RMG-Py.

This commit adds a list of recommended families for setting a 'default,' much like RMG-Java.
It replaces the 'recommended' functionality that RMG-Py was potentially going to have.  
I think this format allows the user to more easily manipulate which families to turn on (even
though we allow more customizable functionality in the input.py file.)