Allow strings in material.add_nuclide in py API
Allow strings in material.add_nuclide in py API

amandalund/openmc,mjlong/openmc,johnnyliu27/openmc,liangjg/openmc,liangjg/openmc,johnnyliu27/openmc,walshjon/openmc,johnnyliu27/openmc,mit-crpg/openmc,wbinventor/openmc,lilulu/openmc,mit-crpg/openmc,mjlong/openmc,shikhar413/openmc,liangjg/openmc,walshjon/openmc,lilulu/openmc,shikhar413/openmc,paulromano/openmc,walshjon/openmc,samuelshaner/openmc,mit-crpg/openmc,shikhar413/openmc,smharper/openmc,walshjon/openmc,kellyrowland/openmc,shikhar413/openmc,wbinventor/openmc,bhermanmit/openmc,samuelshaner/openmc,samuelshaner/openmc,mit-crpg/openmc,paulromano/openmc,samuelshaner/openmc,bhermanmit/openmc,wbinventor/openmc,lilulu/openmc,paulromano/openmc,smharper/openmc,amandalund/openmc,smharper/openmc,kellyrowland/openmc,paulromano/openmc,amandalund/openmc,smharper/openmc,liangjg/openmc,amandalund/openmc,wbinventor/openmc,johnnyliu27/openmc