Unit testing

[tpb1908]

As each of the filters are separate, they should be fairly easy to test.

• Face Highlighter test needs to return correct position when fed an image
• Eye Highlighter test needs to return correct position when fed an image
• Recolour needs to work
• Landmarks needs to work
• Enrolment needs to save images in the correct directory

It would also be useful to have a pre-filter to draw test images on the frame