Also: let the theme service not change classes on document.body but the actual container of the workbench

clean up user data provider

- get product configuration from server

Hello first commit from browser :)

## Problem
We use a custom `vscode-resource` protocol to control access to local resources inside of webviews. This will not work on the web, but we still would prefer a way to intercept webview requests from the main client

## Proposed solution
Move webviews into their own origin and register a service worker on this origin. This service worker can talk with the outer iframe of our webview. When a request for a resource comes in to the service worker:

* In the service worker, add the request to a map and post a message back to the client saying we want to load this resource
* The outer iframe gets the message from the sercice worker and forwards it to our main process
* This process handles the message and use the normal file system api to read the resource (also restricting which files can be read)
* We post the result back into the inner iframe which fowards it back to the service worker
* The service worker now resolves the pending request.

The prototype version in this change works but does not correctly handle multiple clients existing at the same time (plus probably a lot of other edge cases too)