Remove adding src/ to Python path.

Developers already do this to run MouseTrap in place. Easily done
with

    $ source bin/mt-setup

Or more directly...

    $ source bin/mt-add-src-to-pythonpath
Refactor into a class.
Refactor - extracting magic numbers into constants.
Refactor into byte-sized methods that do one thing.
Factor out FaceDetector and NoseDetector.
Refactor FaceDetector and NoseDetector into a generalized Detector.