Catch API errors in hub requests

[TimRiedel]

We should handle errors resulting from hub requests. One way would be to introduce some kind of exception parser, that handles certain http response codes the same way (e.g.) 500, and forwards the errors or parses them to internal ones for other status codes (e.g. 404, because the effect of a 404 might be different per page).

Tasks

• check for which responses codes would this make sense?
• handle these errors in all requests to the hub generically (look at mutations, review-task, review-bar, etc.) --> search for async/await
• implement specific component behavior on error