Adding class for BOW image matcher (Feature #3005).
Same prototype as BOWImgDescriptorExtractor, but do only the matching.
If the feature is accepted, the BOWImgDescriptorExtractor and BOWImgDescriptorMatcher should probably refactor with inheritance.
Add a class to compute the keypoints, descriptors and matching from an image should be added to.
Update PR after mdim review.
Merge remote-tracking branch 'upstream/master' into bow_desc

Conflicts:
	modules/features2d/src/bagofwords.cpp
Remove duplicate functions.
Fix useless space...
Fix name of parameter to have proper documentation.
Fix name of one parameter to fit the documentation.
Fix compilation issue related to previous commit.
Fix the documentation names.
Fix parameter name to fit documentation.
Fix shadow parameter.
Fix default argument.
Merge pull request #1290 from mbarnach:bow_desc