images are resized incorrectly

[goapunk]

Essential Information Images are always resized to 800x600 (4:3) but we sometimes need them in (2:1)
URL: https://gd-stage.liqd.net/de-ls/wie-benutze-ich-diese-seite/
device & browser:
operating system (incl. version):
behaviour: Images are always resized to 800x600
expected behaviour: Images are resized to the correct allowed size (2:1 or 4:3 depening on block)

Additional information if relevant
user role:
important screensize:
Comment/Question:

Screenshot if design related:
Since issues are public, make sure to not display personal or secret data.

[goapunk]

fixed by #950