Remember the most recently downloaded schema

When I open my project and my dev server is not running, I get two errors and autocomplete no longer works. To fix it, I have to start my dev server and reload the window. It would be nice if the extension:

A) used the most recent version of the schema it was able to download
B) didn't show an error popup

```js
module.exports = {
client: {
service: {
name: 'guide-api',
url: 'http://localhost:4000/'
},
excludes: ['**/*.graphql']
}
}
```


Start by tracing the extension's schema download flow for the `client.service.url` configuration when the dev server is unavailable. Reproduce the project-open failure with the server stopped; done means autocomplete continues using the most recently downloaded schema and no error popup appears.

Written by the indexing model from the issue text.