- made some of dependencies explicit
- removed dependencies to highgui and some other modules where possible
- modified some samples to build without modules

For some unknown reason xobjdetect.hpp is included twice.

According to CartToPolar() function documentation, result angles could be in range (0..360). To prevent index overflow this check is important.

- lowered memory usage (now the train use ~3x less memory)
- improved speed (removed some bottlenecks and added fast_log)
- added support to grayscale images
- the LUV features are not computed if the image is grayscale (leads to
an improved detection rate)
- added various parameters (limit_ps, limit_bg, alpha, slidingStep,
is_grayscale)
- added detect() function for a better control of the resize factor