Only reload css file when changed.

[nojaf]

This slightly changes how the browser reloads works. I found myself tweaking the CSS a lot in https://github.com/ionide/FSharp.Analyzers.SDK/pull/89 and was more convenient to only reload the style instead of having a full browser refresh.

Flow:

• You update your CSS file
• The file watcher kicks in and sends a WebSocket message to the browser.
• The message contains the file name and looks for a link tag where the href matches.
• We update the URL by appending a timestamp to the query string.
• The browser refreshes the CSS content without having to do a full page refresh.