For nested sub-images, the origin of the original is kept
Function to get the origin point of a sub-image
Correction of the function to generate sub-images

* The correct parent coordinate is kept.
* Inclusion of the pixels of the border (following the BoofCV doc).
* Using width and height are less ambiguous than x1 and y1.
Minor changes; removal of useless code
Tests for sub-images: ok