Implemented Request #478, Histogram backprojection, in a basic way.

New class: colorHistogram to store hue-saturation histograms
Method for smoothing the histogram.

New methods of class Image:
colorHistogram(ROI, huebins, satbins) - generates histogram from region of interest
backProject(histogram) - backprojects image using histogram, as requested in 478
findBlobsFromHistogram - finds blobs; one-liner.

Functions are mostly wrappers around the openCV functions cv2.calcHist and cv2.calcBackProject.

Functions not yet as flexible as they could be regarding what arguments they take.

Automatic tests (for nose) were outlined, but not yet written. Plan to do this over the weekend.
Manual testing was done during coding; functions seem to work.
Test suite checks out OK.
Merge branch 'develop' of github.com:Play84/SimpleCV into develop