Add _parse_str_to_list method in FastaSerdeMixin and Fix unit test fails

[yamasampo]

• Add _parse_str_to_list function to convert list-like string to Python list. This function is replaced with eval function used in from_fasta classmethod.
• Fix unit test fails in functions in aln/tests/test_alignment_constructors.py. test_none and test_with_ids_no_descriptions in TestMakeRowMeta failed because not empty DataFrame but DataFrame with "" value was assigned in case of no row metadata or descriptions. This was fixed by returning pandas.DataFrame(None, index=range(self.nrows)) and pandas.DataFrame(None, index=ids) for each case of no row metadata and no descriptions.
• Add unit tests for utils.py as alignmentrs/tests/test_utils.py. This needs to be updated especially for parsing description lines. Maybe this test should be in aln/tests/test_alignment_constructors.py?