Price deletion should also trigger associated price_tag status update

[TTalex]

What

• When a price is linked to a price_tag, removing said price (using API) clears the price_tag price_id but does not reset the price_tag status
• This leads to a price_tag with status set to 1 ("price is already linked for this price tag"), but no valid price_id

Expected

• status should be set to null, since "only price_tags with null status will be suggested in a "Hunger Games-like" games"

Part of

• Add a price_tags table to store predictions #611