Feature/fc equispaced vtu

This MR is to introduced equispaced output into the VTU output. So the option -m equispaced output can now be executed, i.e.

FieldConvert -m equispacedoutput file.xml file.fld file.vtu

will produce a much reduced set of points when using tris or tets which also gives a more even rendering of the image

The MR also contains the ability to run it in parallel which produces a .pvtu file that allows multiple output files from each partition to be loaded into ParaView of VisIt. The current convention for this is to generate a directory file_vtu which contains file P0000000.vtu P0000001.vtu ...

Currently it does not check if the directory exists before dumping files.