fix a variety of bugs including a memory leak in the genie handler

This commit fixes a number of compiler warnings and issues, mainly:

• Clear GENIEInputHandler::fGenieNtpl between events to prevent memory fragmentation, which was causing huge memory usage in nuismin
• Removed some unused variables
• Fix a few possible null pointer dereferences
• Fix a few small memory leaks with mismatched new/delete/delete[]