Feature/cache sample queries

[Woozl]

A simple way of caching the responses for the 5 sample queries on the main page. Closes https://github.com/RobokopU24/Feedback/issues/173, although we may want to look for a more robust solution.

Downsides:

• will get out of sync with the KG eventually, requiring the file to be manually updated
• will not scale well to a large number of queries