Enable customizable colors for cell and boundary regions to gridplot#115

Da-Be-Ru wants to merge 2 commits intoWIAS-PDELib:mainWIAS-PDELib/GridVisualize.jl:mainfrom

Da-Be-Ru:feature/regioncolorsDa-Be-Ru/GridVisualize.jl:feature/regioncolorsCopy head branch name to clipboard