Vulnerability search engine migrated to MongoDB

Since RethinkDB only offers slow count queries which don't perform very well in production and also CouchDB's Mango queries are quite slow, the database of the vulnerability search engine has been migrated to MongoDB which has a great performance on big data (>150k of vulnerability JSON data) and offers fast count queries.

Also a custom query caching function has been implemented to cache the result of count queries and make the website even more performant.