Caching of feed data

Loading feed data live on every request has many disadvantages:

• It is slow
• It produces load on the AlekSIS server and on the feed's server (imagine a whole school of 2000 students and 200 teachers firing up ALekSIS first thing every morning and hitting a WordPress somewhere...)
• It breaks when the RSS backend is offline for some reason or produces errors

Using django-feed-reader might be one option to solve this.