Issue Tracker Email Notification Selection Option (BB-7713)

Would love the option to be able to select who receives email notifications on an issue by issue basis. Similar to how Basecamp allows you to select people whom to email. This would be helpful as not all issues require an email notification to the whole team, and it just adds to cluttered inboxes.

See basecamp example here - http://cl.ly/image/0g1L100f1k2A