Adds fastNlMeansDenoisingColored a better denoising algorithm

[JLLeitschuh]

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[codecov-io]

Codecov Report

Merging #847 into master will increase coverage by 0.02%. The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master     #847      +/-   ##
============================================
+ Coverage     52.35%   52.37%   +0.02%     
  Complexity     1134     1134              
============================================
  Files           240      240              
  Lines          7724     7736      +12     
  Branches        526      526              
============================================
+ Hits           4044     4052       +8     
- Misses         3494     3498       +4     
  Partials        186      186

[SamCarlberg]

Screenshots/examples please