Protocol for when email digests are sent

[yoavartzi]

Users should receive the weekly digest in the following cases:

• [x] If there are any new recs from the users they follow
• [ ] If there are no new recs from the users they follow and they didn't put a recommendation the past 3 cycles and they didn't receive an email from this option for 4 cycles -- the email should say there are no recommendations, ask them to recommend a paper, suggest to follow more users, and give them a random rec from the current cycle

I would like to see examples of the emails look for the two cases, so we can refine the language.

Thanks!

[yoavartzi]

First implementation: if there's a rec, email, otherwise -- no email