Drug Overview: add a general entity overview

[HermannKroll]

At the moment, users can search for entities in the Drug Overviews that are no drugs, e.g. https://narrative.pubpharm.de/drug_overview/?drug=mmp-7

Users may be confused why an overview is shown although no ChEMBL information is available. We need to rework the process. If users query for a string that does not correspond to a drug on ChEMBL, we should inform him that the search yields no results but we can forward him to a general entity overview. We call it "Overview". Here, we show structured lists similar to the drug overviews but with slightly different queries. The overview should NOT include any card view of ChEMBL data and NO drug-target-disease network and NO keywords, but should contain structured lists plus recent publications.

[HermannKroll]

Needs to be approved by experts.