Get the last block processed
    Return the integer on success
    Return None on error

def get_last_block(working_dir):
    """
    Get the last block processed
    Return the integer on success
    Return None on error
    """

    # make this usable even if we haven't explicitly configured virtualchain 
    impl = sys.modules[__name__]
    return BlockstackDB.get_lastblock(impl, working_dir)