In response to Bug #2927 

change to reject contours with moms.m00 = 0.0
contours with zero area rejected

reject contours with zero area by using the "continue" statement to be in sync with the condition checking style used in the whole file
update libwebp up to 0.3.0
fixed compilation after CV_IMPLEMENT_QSORT_EX removing
Merge pull request #722 from gpsinghsandhu:blob-detector-cpp
Merge pull request #737 from AoD314:webp2
Merge pull request #746 from jet47:fix-gpu-compilation