Add "logs" UI

[kentcdodds]

I tell people to open the playground in a separate instance of their editor from where they're running the server, but the log output shows up in the server that's running the workshop app. This will make it pretty confusing for people looking for the logs.

I think we should pipe the server-side logs to the client.

Maybe similar to how in-browser editors do it:

It's a resizeable/dismissable panel. I would stick it at the bottom of the preview area. It should only show up when the app is running. We can probably reuse some of the code we have for the test output piping.