Lazily load problem data

[borkdude]

The data in data.cljc is effectively JSON / EDN. We don't need to load all this data in the first page load, but only the problem titles. Once you navigate to a problem, you can then load the problem data and show some other solutions when the problem is solved (these solutions could be contributed through PRs). I propose to store every problem in a separate JSON file that can be fetched using an HTTP request to implement this lazy loading.