Added handling of several corner cases

[spoenemann]

I restructured the processing of incoming and outgoing messages so we can handle more corner cases:

• Catch errors and forward them to the result promise (for requests) or log to console
• Forward messages from a webview to another webview
• Requests to multiple webviews (webview type as receiver) enter a race where the first response wins
• Support webview panels (API is the same as webview views)

I also deleted yarn.lock and updated package-lock.json as we currently use npm, not yarn.

[dhuebner]

First PR 🥇