Update formats.py and repository_tool.py.

repository_tool.targets.delegate_hashed_bins():

Edit comments, add logging information, and rename 'max_number_of_bins' (now 'total_hash_prefixes') for clarity.
Fix expected value of 'number_of_bins' (power of 2 instead of multiple of 16.)
Remove the 'self' argument in get_filepaths_in_directory() (now a staticmethod.)

formats.py:
NUMBINS_SCHEMA may now start from 1 (allow the creation of 1 delegated hashed bin.)