Adds Edge-Preserving Filter (#1690)

* Module EPF - Edge-Preserving Filter added

* Changed name from template to epf

* Removed clang-format file

* Added header Files. Eliminated showWindow function. Used CommandLineParser.

* Moved filter from epf module to ximgproc

* Removed header files from sample

* Minor bug fix in demo. Pointers in demo removed.

* Pointers removed. InputArray/OutputArray added

* License header added

* License header from sample file removed

* Unit test for performance added

* Replaced manual mean computation with cv::mean

* Beautified code via clang-format and https://raw.githubusercontent.com/opencv/opencv_contrib/master/modules/cvv/.clang-format

* Merged historic if... else if statement into one if statement

* Trailing whitespace removed and .. changed into .

* Tabs replaced with 4 spaces.

* Removed subwindow = src(roi);

* Moved type test to beginning of code

* Removed indentation from namespace and added //! @}

* Added name to header

* git cleanup introduced some errors fixed here

* Changed path testdata/perf/320x260.png to perf/320x260.png

* Fixed warning declaration of 'subwindow1' hides previous local declaration

* Fixed warning 'const' qualifier on reference type 'cv::InputArray' (aka 'const cv::_InputArray &') has no effect

* Accuracy test added/

* Renamed void edgepreservingFilter to void edgePreservingFilter