Add support for JWKS

[basvanbeek]

Would be great to allow providing JWKS as input and validating the signature by pulling the right JWK from the set by parsing the kid.

Feedback on the new vs old UI:
I think the new UI is an improvement over the older one. The older one looked clunky and the new ability to inspect claims tables with explanation will help novices to understand more as well as providing a nice decoded human readable view on time properties like iat, exp, nbf, etc. This works better than the old hover over.

Dark mode helps to keep it in line with the rest of my open applications.

Would be good to allow the "What is a JWT?" and "Warning about JWTs" sections to be persistently removable (local storage?). People tend to come back to this tool and have read and understood these concerns. They clutter the view for those knowing the tool.