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
fix CUDA LUT implementation

In CUDA 6.0 there was a bug in NPP LUT implementation (invalid results when
src == 255). In CUDA 6.5 the bug was fixed.

Replaced NPP LUT call with own implementation (ported from master branch) 
to be independant from CUDA Toolkit version.
Merge pull request #3164 from jet47:fix-cuda-lut
Fixed crash in SSE implementation of FREAK descriptor when number of pairs is set to something other than 512.

See http://code.opencv.org/issues/3889 for more details
Merge pull request #3178 from jimcamel:freak_sse_bugfix
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