Unpack material metadata when loading a file

[gonuke]

Currently, DagmcFile loads basic DAGMC data about a model upon opening the file. It will be useful to also load the material metadata and create a mapping of materials to volume entity handles and/or IDs.

Parse the material names from the group names and populate a dictionary of 'material_name' => [list of entity handles]

[shimwell]

There is some code in here that might be handy for finding volume ids, material tags and the linkage between material tags and volume ids.

https://github.com/fusion-energy/dagmc_h5m_file_inspector

Also here https://gist.github.com/gonuke/c36e327e399c7a685cd315c738121c9a

[gonuke]

And now here: https://github.com/fusion-energy/dagmc_h5m_file_inspector

[gonuke]

Two modes for the user to access this data:

• query which material is in a given volume ID or EH
• query which volumes contain a given material

A dataframe that with columns vol_eh, material_name can be used to satisfy both queries