Require on client side

In order to share modules between the client and the server:
- creating folder client/node_modules
- when requesting client/node_modules the server returns a wrapped
version of the files
- Files in nodesite/node_modules are accessible via client/node_modules
as if they were in the client folder
- renamed route into demand and clarifying it
- introducing js/module.js
- moving lot of client/js files into nodesite/node_modules and
client/node_modules
- creating a server folder