VSCode extension icons are not loaded when a path is added to base URL

Bug Description:

Steps to Reproduce:

1. Run sample browser-app with a vscode extension. I'm using docker for vscode extension which I got from the public github.
2. Open http://localhost:3000
3. Plugin will be loaded with the icon on the activity bar:
4. Open http://localhost:3000/index.html , you'll observe that icon wouldn't be loaded. Network call:

Request URL: http://localhost:3000/index.html/hostedPlugin/docker_vscode/resources/activity-bar-icon.svg Request Method: GET Status Code: 404 Not Found

If you see the above get URL, extension is using http://localhost:3000/index.html as the base URL to fetch the extension assets. How do we configure theia to ignore index.html in the path while fetching the assets for an extension?

Additional Information

• Operating System: OSX
• Theia Version: 0.14.0