It made recognising incorrect entries needlessly slow

return goes back one frame up the stack
next goes back to the closest frame on the stack that supports the
operation (that is close enough in RefSeqGPFFParser alone)
It works unless I subclass create_xrefs, and then my Hive workers die:

Lost control. Check your Runnable for loose 'next' statements that are
not part of a loop       WORKER_ERROR

- New xref: to a WormBase CDS feature
- Modify WormbaseCElegansRefSeqGPFFParser to serve both kinds of files
- extract a utility method from RefSeqGPFFParser
- xref_config.ini stanza for wormbase_cds
- tests for new functionality

- maintain naming convention: WormBase specific stuff says Wormbase at the front
- rewrite WormBaseDirectParser
- WormBaseDirectParser populates protein_ids
- superclass method to make dependent protein_ids as parent
- tap into UniProtParser
  + also skip EMBL scaffold ids (we can't reliably assign them)
- tap into RefSeqGPFFParser
  + extract a method
- tests for new stuff
  + add %args to parametrise test_parser

Benefits for RefSeqGPFFParser:
RefSeq proteins have coordinates as part of their identity, so we
can't reliably sequence match them, we will also pick up all paralogs.
This change fixes this spurious mapping.
Benefits for UniProtParser:
Not the above: UniProt entries are not tied to coordinates so all
paralogs map to the same entry. We can handle versioning and updates
a bit better: if WormBase updates an entry and a protein id changes but
UniProt doesn't reflect this yet, with the change we will still pick up
the UniProt entry although we can't sequence match any more.

The only part of the xref-mapping pipeline that depended on the
long-deprecated module XML::Simple was TAIROntologyParser - which did
not actually *use* that module for anything. Get rid of the useless
import, thus making it unnecessary for XML::Simple to be mentioned in
the cpanfile.

+ XrefParser::Database stores a DBConnection, setters delegate to it
+ New test database, for xrefs
+ Setup to test XrefParsers
+ Tests for WormbaseDirectParser

- Update RefSeqCoordinateParser such that it fetches the RefSeq accession either from the stable_id or the display_xref in the otherfeatures database.

Fix to fix in commit f9dc4756 (ENSCORESW-462). info_text should not have been null'ed by default as the column is NOT NULL.