* change url to hide app behind a relative path

* pass some of ther server configuration through to the client

* serve static files and connect to socket.io correctly when a URL Prefix is set

* Revert the changes to opengraph meta tags

opengraph meta tags need to be absolute URLs

* Remove unused commented-out code

* fix background.png url

* use prefix path for open graph metadata

* Revert changes using server side url modifications

* get open graph and socket.io url from request url / window.location

* remove debug console.log

* Fix favicon when not running under "/"

* Add proxying instructions to the README

Co-authored-by: Laurent Mazet <mazet@softndesign.org>
Co-authored-by: ophir <pere.jobs@gmail.com>