Limit returning entries per feed/source

[johanneshiry]

At the moment, the api endpoint for feed doesn't provide any possibility to limit the number of entries per feed (e.g. provide only 3 elements of each source/feed we get the data from). Would be nice to have this feature to prevent having only data from e.g. John Hopkins University because our other sources didn't update their data for some days.

The exact specification why and how we want this feature still needs to be discussed and described before implementing it.