added mask support to cv::norm, cv::meanStdDev
added some performance tests
added cv::PSNR performance test
added NORM_L2SQR type to cv::norm
changed code in python tutorial, these functions don’t return image
Merge pull request #2121 from ilya-lavrenov:tapi_perf
Merge pull request #2138 from alekcac:python_tutorial_fix