Fix#820
Ok, so after I would have to use the same method in three different
locations (`<ds-card>` expects an `image` attribute but cannot render
entire components) I decided to implement the prefix of image urls with
a filter rather than a component. The downside of this is that we have
to add the filter on a lot of component tests. The benefit is less
components and hopefully less complexity.
@ulfgebhardt I refactored the mixin because it's not enough code to
justify the additional complexity. If it's just two lines of code, I
find it the best solution to use a computed property.
You can use components and computed properties excessively, they tend to
be easier to maintain in the long run.
See:
https://github.com/Human-Connection/Human-Connection/pull/478/files#r281267486
> We found the reason for it: If you have an exclamation mark in the schema e.g.
> email! and the response would e.g. expect the email for each User object, and
> the server does not have an email for the client, then the entire User object
> gets nullified.
