Add a `--notax` flag to SqueezeMeta, sqm_reads and sqm_longreads

[fpusan]

... and make sure downstream scripts can handle it, including:

• The rest of the SqueezeMeta pipeline
• sqm2tables.py
• sqmreads2tables.py (is there a sense to allow using queries for filtering if tax is not present?)
• SQMtools??