Extension hangs when server is busy

[kevinhalliday]

When the server is busy handling a bunch of requests (particularly when it needs to proxy those requests to a remote rpc endpoint) the extension will hang with a loading indicator on open.

The extension relies on a GET /forks on open for a few reasons - check to make sure the server is running, and check to make sure the extension is using a fork that's available. This GET hangs when the server is busy, hence the loading indicator. We could rework extension ST it does not rely on a successful GET /forks to open.