Add Background-Image

[btemperli]

Option to add a background-image for the claim (only the claim without the logo - text left, text right and claim text).

for a good usability, we move this to a seperate page.

As mentioned in #17.

[wp99cp]

Sound's good. I'm happy to help once I find some free time.

I have a feature request related to that. However, it is more a design/CI question: We should add an option to use the claim on white background. Potential use case: on printed documents, e.g. a Picasso: