Unify ImageReader/Writer and VTKmDataSetReader/Writer interfaces

Currently VTKmDataSetReader and VTKmDataSetWriter take the file as an argument in the constructor and have a separate read/write method that does not take arguments, whereas ImageReader and ImageWriter take no arguments in the constructor and take the file argument to the read/write methods. The ImageReader and ImageWriter classes should be updated to have similar interfaces as the VTKmDataSet classes.