Cache annotations & separate thread for webservice requests

[matthiaskoenig]

The webservice request should not block the views.

• [x] cache query results as optimization
• [ ] perform query in task and use channels for update

Some resources on this: https://docs.djangoproject.com/en/2.0/topics/cache/ https://www.fullstackpython.com/caching.html https://realpython.com/blog/python/caching-external-api-requests/ https://requests-cache.readthedocs.io/en/latest/index.html

We don't want to cache the webpages, but only the information for given annotations. These should expire after some time. The perfect solution for the problem seems to be the requests-cache which allows to use redis as a backend and supports expiring.