Can create training set in PNG format

The format of the training set can be changed with the `-pngoutput` key.
Output image will be resized to a 640x480 size if greater.
Typo in string fixed
Class naming update
Documentation improvement
Bug in output format for JPG set fixed
Naming fixes and code beautification
No output image resize in case of PNG dataset
Documentation update: createsamples usage
Include for cvSameImage corrected
Warning on converting int to bool fixed
Merge pull request #3156 from sergregory:CreateSamplesMod