Entity cache pile-up if vehicles frequently change IDs

[testower]

There seems to be a performance issue in redis that occurs when consuming feeds (free_bike_status) with vehicles ("bikes") that frequently changes IDs. E.g., all vehicles have new IDs on every update. This was the case with some of our feeds recently.

As a temporary measure, I have made it possible to leave individual feeds out from the aggregated api, using the "aggregated" field on the feed provider config (aggregated: false) in #211 .