added nuclides split for tallies

[shimwell]

Proposed changes

Not ready for review

@bruceey42 this adds the ability to split up tallies by nuclides.

I need to check the post processing still works and add tests but this PR is progress towards your feature request

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Pep8 applied
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)