Add proxy to access local files

In 4.1.0.Alpha2, static files can be accessed from the local browser using the file:// scheme.
These files could also be accessed from the embedded web server (see if the default 35729 port can be reused), so that static files can be accessed by remote devices. In that case, the livereload script could be automatically injected at the bottom of html pages.

This proxy only allows for access to files in the workspace, it MUST NOT let some browser access files out of the workspace.