Renamed SurfaceMGXS class to MeshSurfaceMGXS
Renamed SurfaceMGXS class to MeshSurfaceMGXS

liangjg/openmc,walshjon/openmc,paulromano/openmc,shikhar413/openmc,mit-crpg/openmc,mit-crpg/openmc,shikhar413/openmc,liangjg/openmc,mit-crpg/openmc,paulromano/openmc,liangjg/openmc,shikhar413/openmc,amandalund/openmc,walshjon/openmc,paulromano/openmc,amandalund/openmc,walshjon/openmc,paulromano/openmc,mit-crpg/openmc,liangjg/openmc,amandalund/openmc,walshjon/openmc,amandalund/openmc,shikhar413/openmc