Issue 3472 script to auto install node modules

This small script is aimed to clone the browserid repository and install node 0.8.12 and all its necessary modules. 
Node 0.8.12 is installed through `nvm` which allows to install and use different versions of Node on the same system.

The script currently runs on Ubuntu 13.04 and Debian 6.0.x

Usage : 
 - `./setup_node.sh install <directory_to_clone_browserid> <directory_to_install_nvm>