Email Previews, Logging, and Latest 9 Posts

A minor bug was resolved where the new Send Preview functionality would on occasion request a preview to be sent multiple times. We now only request the preview to be sent once.

In addition, we now log all email preview sends internally to improve internal support of our customers.

Lastly, you can now merge fields in for now just the most recent 5 posts, but the most recent 9! For customers that send more of a digest model and have lots of content, you can now include much more in your FeedBolt template.

Commit #f3da58d