Append the observation messages to feedback mail

[KaraMelih]

If the user has published an observation message within the last 24 hours, this information can also be added to the feedback email.

Following the discussion in #11 we figured that it is easier and more secure this way.

We need to write a mongo query which checks if there was an "Observation Message" within the last 24hours, when the user requests a heartbeat feedback. We then add that information on top the feedback and send the email.

This way, the user can get a "delivered confirmation" without any danger.

[KaraMelih]

@Storreslara could you take care of the MongoDB part for this?
We need "find entries within last 24h from experiment X" functionality. Then we can append that info to the image.

This would look something like this on the feedback image

[Storreslara]

Yeah let me get something together