added OpenCVFindIPP.cmake script, which will look for IPP installation at CMake configuration time. First, IPPROOT environment variable will be tested, if not found script will look at default install places.
The script should support IPP from 5.3 up to 7.x versions (although tested on Windows for IPP 6.1 and IPP 7.0 versions only)

Preliminary optimization of HOG with IPP added too. Not yet quite efficient, code for cpu branch should be redesigned in order to have better performance.