TEST: add test for contrast filter

.../Applications/AppFiltering/app/otbContrastEnhancement.cxx

Modules/Applications/AppFiltering/test/CMakeLists.txt

Modules/Filtering/Contrast/test/CMakeLists.txt

Modules/Filtering/Contrast/test/otbApplyGainFilter.cxx

...tering/Contrast/test/otbCLHistogramEqualizationFilter.cxx

Modules/Filtering/Contrast/test/otbComputeGainLutFilter.cxx

Modules/Filtering/Contrast/test/otbComputeHistoFilter.cxx

Modules/Filtering/Contrast/test/otbHelperCLAHE.cxx