writing material name in OpenMC material file

[shimwell]

Currently it looks like the OpenMC material writer only writes the material id in the materials.xml file

It would be handy if the material name was also included

I have created a new branch that can do this

Unfortunately I based it on the Serpent additions so I shall make a PR once those serpent additions are merged

[shimwell]

I have added some code to write openmc material names out along with the material ID. It appears OpenMC is case sensitive so I was thinking about retaining the case when files are read in and converted. What do you think would this cause to much trouble.

for example reading in a serpent material card when materials have capital letters in them and writing to OpenMC, should we retain the capitalisation?

[makeclean]

This was addressed by #18