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() // Returns all attachments
  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(); // Returns all attachements
  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)
- Include #535 it's not a good practice to use `'http:method'` at route level but it may be better to not let it buggy.