Make Python scripts compatible with Python 3

This pull request makes necessary changes to Python modules/scripts in src/utils and elsewhere to run with either Python 2 or 3. Most of the changes were pretty trivial: making sure the print function is used, wrapping dict.keys() and dict.values() with list() where necessary, importing the correct modules (e.g. tkinter vs Tkinter), etc. All the shebangs now read `#!/usr/bin/env python`. I also removed two scripts that are no longer needed.

@nelsonag Can you review this? You may be the only brave soul who is using Python 3 as their default interpreter.