Support writing binary files to legacy VTK files

The legacy VTK file writer writes out in ASCII. This is helpful when a
human is trying to read the file. However, if you have more than a
trivial amount of data, the file can get impractically large. To get
around this, `VTKDataSetWriter` now has a flag that allows you to write
the data in binary format.
10 jobs for write-binary
Status Name Job ID Coverage
  External
passed cdash-buildbot

passed vtk-m-dragnipur-osx-shared-debug+32bit_ids+64bit_coords+clang+tbb

00:01:15

passed vtk-m-dragnipur-osx-static-release+64bit_coords+clang+tbb

00:00:16

passed vtk-m-osheim-windows-shared-debug+ninja-vs-2017+tbb

00:06:16

passed vtk-m-osheim-windows-static-release+ninja-vs-2017+tbb

00:00:38

passed cdash-buildbot

passed vtk-m-dragnipur-osx-shared-debug+32bit_ids+64bit_coords+clang+tbb

00:01:24

passed vtk-m-dragnipur-osx-static-release+64bit_coords+clang+tbb

00:00:23

passed vtk-m-osheim-windows-shared-debug+ninja-vs-2017+tbb

00:06:09

passed vtk-m-osheim-windows-static-release+ninja-vs-2017+tbb

00:01:32