Add scope to `lithium\net\http\Router` and `lithium\net\http\Media`.
- Routes can be scoped using the following notation:
  Routed::scope('); // Returns the current scope
  Router::scope('name'); // Use a new scope
  Router::scope('name', function(){/* executed inside the scope */});
  Router::attach('name', array(), array()); //Attach a mount point to a scope
  Router::attached('name', array()); //Returns the attached mount point configuration
- The Media class can be scoped using the following notation: (i.e. usefull for CDN or others media location).
  Media::scope('); // Returns the current scope
  Media::scope('name'); // Use a new scope
  Media::scope('name', function(){/* executed inside the scope */});
  Media::attach('name', array()); //Attach a mount point to a scope
  Media::attached('name'); //Returns the attached mount point configuration
- Modifiying the Media::webroot() signature (BC Break)
- The paths of assets paths now called 'paths' for consistency see `Media::_asset` (BC Break)