Added gaussianmixture and backgroundGM (unused)

Use OpenCV EM -- may be too slow for real time
Use Background::setup to initialize
Removed obsolete Classifier, moved Background to World
Update plotsnap.m to not use vis.class
Added mixtest to Makefile
Typo in debug message
Added assignments arg to Background::update to limit updates to those points classified as background
Have background return likelihoods (from like()) instead of probs (from isbg()); store result in World
Put bglike in mat file
Pass bglike into Person::update() and use for computation
Treat a low-likelihood target as if it was invisible, don't update measurements
Changed default movie suffix
Removed some unused parameters
Background updates (was pending for a while)

Still forcing all points to be updated.