Add an option to start the server without opening a browser

[amxmln]

It would be great to be able to "go live" without a browser popping up. The old atom-live-server had a no-browser setting that prevented the browser from opening when starting the server if set to true.

Background: I like opening the live server in a new VS Code tab with the "Simple Browser" command, or in an Incognito window of different browsers without always having to change the config.

Thanks for your hard work on this! 😊