This is code that needs to be repeated in possibly several places
(website, API, tests), so it makes sense to have those "high level
actions" a bit abstracted. edit.edit_images was already doing that to a
certain degree, but the code shouldn't have stayed in the view.

To add more playwright tests and to cut down on the duplicated code, the
helper methods have been put into a small class. This way, we don't have
to add 100 pytest fixtures.