Make all OpenMC names case insensitive

PyARC input is more case-insensitive than I originally thought and more bugs have come to light with names not matching across various inputs (ie an assembly can be named Assembly1 but then referred to as assembly1 later and vice-versa). This MR fixes PyMCSim such that all names of materials, blends, surfaces, subassemblies, and assemblies are case insensitive (adding .lower() everywhere). Once all names are processed by PyMCSim, they should all be lower case now. I think I caught all the places to fix this issue. The prerun test is updated with just some various capitalization differences to hopefully catch these all.