Favicon + static content

* Added a static folder under client to serve static files
* Moved images, sounds, index.html and favicon to static folder
* gulp task to copy static files over to build
* changed serving of static files from the build folder instead of client, which was exposing way more than needed
* With index.html in the static folder, there's no need for the catch all route that returned index.html

Tested it manually and all seem to work fine. Hope I didn't miss anything...