Fix hashbang on python scripts

Convert ```#!/usr/bin/python``` to ```#!/usr/bin/env python``` at the top of all python scripts. 

> Running a command through /usr/bin/env has the benefit of looking for whatever the default version of the program is in your current environoment.

source: http://stackoverflow.com/questions/16365130/the-difference-between-usr-bin-env-bash-and-usr-bin-bash