Update filter on is_aa_seq_valid

[LuppovDaniil]

Filters should include C in the begining and F/W at the end

def is_aa_seq_valid(aa_seq: str) -> bool:
    """
    :param aa_seq: amino acid sequence to be validated
    :return: sequence valid or null
    """
    if pd.isnull(aa_seq):
        return True
    return len(aa_seq) > 3 and bool(re.match(r'^[ARNDCQEGHILKMFPSTWYV]+$', aa_seq))