A user can add the same data directory path multiple times to a dataset

[ethanandrews]

When adding a new data directory to a dataset, it's possible to add the same data directory path multiple times, there doesn't seem to be any validation of whether a new data directory already exists. This is the case either through the Django management command, or using the web UI.

[joefutrelle]

@mike-kaimika I think the appropriate unique constraint, plus a UI to provide feedback on errors, should do it

[mike-kaimika]

This should be all set. The attached PR adds the unique constraint, which handled the UI validation. I also added validation to the management command