Initial addition of ba_class, an alternative to SPRdataclass.  This class, ba or Biosensor Array, has one internal structure rather than different internal structures depending on whether SPRit or Biacore or other data was imported.  This makes the code smaller and more readable.  It provides default values, usually 0 or null text, that make it easier to import and export different file formats.  We also add io_module to provide import and export features.  We also add test.py as a convenience for testing and demonstration.