[io] Add RasterImageReader

dumux/io/CMakeLists.txt

dumux/io/rasterimagereader.hh

test/io/CMakeLists.txt

test/io/rasterimagereader/CMakeLists.txt

test/io/rasterimagereader/blackwhite_binary_j.pbm

test/io/rasterimagereader/blackwhite_j.pbm

test/io/rasterimagereader/blackwhite_j.txt

test/io/rasterimagereader/grayscale_binary_j.pgm

test/io/rasterimagereader/grayscale_j.pgm

test/io/rasterimagereader/grayscale_j.txt

test/io/rasterimagereader/test_rasterimagereader.cc