Board Export : include the internal card number in the export#72

By having the card internal number (for example, the ones shown by the Card number power up by Reenhanced) included, it becomes easier to refer to individual cards. This lets us treat the cards in a similar manner as Jira tickets and simply refer to card #xxx.

This is useful for organizations that use Trello cards in a software development process, where individual cards develops and changes along the way, including the title.