trends now available (route '/trends'). cronjob sends request to twitter api (every 10 minutes) and saves latest trends in DB.
trends collection: keep size under 4 items (latest three trend-objects available). delete older entries if size > 3.
Revert "trends collection: keep size under 4 items (latest three trend-objects available). delete older entries if size > 3."

This reverts commit 10ca5bf80828d0025783069b2f7ad2063edd76d7.