plus minor edits and fixes

Reverts "Set the default value of exposure_weight in createMergeMertens to 1.0" because it breaks source code compatibility and tests
This reverts commit dbfd6a3d.

Changed parameter type of fastNlMeansDenoising[Multi][Abs] from std::vector<float> to const std::vector<float>&

Changed fastNlMeansDenoising and fastNlMeansDenoisingMulti back to sum of sq distances. Moved sq sum of abs distances to fastNlMeansDenoisingAbs and fastNlMeansDenoisingMultiAbs

removed optim module; moved its functionality to core and photo modules; moved drawing functions from core to imgproc. Removed FilterEngine etc. from public API

Removed conflict

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Removed opencv_extra folder inside opencv folder

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