Expand worm database to include multiworm capability

[MichaelCurrie]

Moving this issue to this repo, from openworm/open-worm-analysis-toolbox#194.

[MichaelCurrie]

This will be necessary to keep a 1-1 mapping between a row in the "experiments" table in the database, and a WCON file, since WCON files can have multiple worms.