Add HaarLoader and ImageConverter

This adds a HaarLoader class which will load a haar file based on
a predefined name.  This will cache the loaded haars within the
thread, so they will not be constantly loaded.  Haar cascades can
be loaded from files and cached to the thread using an optional
cache name.

This also adds basic ImageConverter class which will convert images
from RGB to grayscale.  Later this will be used for other imaging
related tasks.

These, like many things which will be committed tonight, need some
tests to back them up.
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.
Move FeatureDetector and NoseLocator into vision, and run.py into mousetrap.nose_locator_sample.
Convert comment into code.
Fix undefined variable.
Add Image to ecapsulate conversions.
Use NoseLocator to main.
OK, the pointer moves. This needs cleaning. But at least it runs.
De-linting
Improve design of Camera and Image.

* Add defaults to camera constructor.
* Make Camera.set_dimensions public.
* Add Image.get_width and Image.get_height.
Move Pointer int moustrap.gui.
Moving test_*.py to tests/.

Having tests in the same directory is cluttering up my mind.
Give me a good reason that I haven't thought about and I'll
consider putting them back.
Add bin/mt-clean.
Add moustrap.gui.Gui to collect public mousetrap.gui functions.
Encapsulate screen access into moustrap.gui.Gui.