Added SNANA CC SN models and Whalen PopIII models.
   * all the data files are added under ../data/models/ccsn and /whalen
   * total size of all data files = 220M
   * test/test_models.py:  new unit test for new models
   * data/models/snsedextend.py : stand-alone module for extrapolating the SNANA CCSN SEDs