Allow user to select how frequently they wish to receive email updates on ideas they have subscribed to or voted for. Merged

Feedback from our customer:

Pretty frequently, I receive a flood of emails to my inbox when there is an update on an idea I've voted for or entered. One person will make a comment, then many other people on the idea will respond, and for each one, I receive a separate email. I've discovered that I really don't need a minute-by-minute update on these. It would be much appreciated if you could add a user selection in the email preferences for a "daily digest" email instead of an email for each update. That way, I could still keep tabs on certain ideas, but not have my workday interrupted by deleting scads of repetitive (and often largely irrelevant) emails.