Delete trello card associations less aggressively

When a user is working on a feature in Aha that is linked to a Trello card, if she accidentally changes the release for this feature to the release of a different product (e.g. the Demo Fredwin cycling product), the trello linkage is immediately deleted and lost forever. Since it's not possible to manually relate an existing Aha feature to an existing Trello card (only to create a new Card or a new Feature), the clean-up from this mistake is really painful.