Devcards development tool

Devcards (https://github.com/bhauman/devcards) make it easier to quickly develop new UI components in re-frame without needing to have the data serving it in place. It also makes it possible to reference these devcards when you later need to test whether changes don't break the UI in a specific state. (Kind of analogous to TDD, just for visual UI instead.)

I have used something similar in JS (Storybook) and thought it invaluable, so I think we should give this a try here as well!

Review Devcards and the existing re-frame UI setup; the issue provides no file or test entry point. Before implementation, define how cards would be integrated and what UI states must be covered, since no completion criteria are specified.

Written by the indexing model from the issue text.