[TAV-374] Fix the model associations in TavernaPlayer::Run.

These were specified with contants but need to be strings to avoid premature
initialization.
[TAV-374] Formalize the workflow/run association.

A workflow has many runs and a run belongs to one workflow. This was already set
up in the tables but not formally declared in the models.
[TAV-374] Formalize the run/run_port association.

This was already declared in one direction, so this closes the loop.
[TAV-374] Formalize the run/interaction association.

This was already declared in one direction, so this closes the loop.