Update sallseqid attribute of BLAST tab results to create list

This field may contain multiple values, so a list is a more proper data
structure. The list is turned back into a string upon writing to a file.
Add parsing support for BLAST 2.2.28+ tab fields and its tests
Fix blast-tab bug where str(SeqRecord) instead of str(SeqRecord.seq) is written
Add new test for BLAST commented tab writing