More program tests + change ccl_program_save_all_binaries API

Program tests added:
- ccl_program_get_all_devices()
- ccl_program_get_num_devices()
- ccl_program_new_from_binary_files()

Change in ccl_program_save_all_binaries() API:
- This function now accepts a location where to put the saved
binaries filenames.