addJavascriptModule, RequireJS (dependency management)

Following the thread, this is the PR to add support for RequireJS (dependecy management)

* With this new JDocument method, a set of Javascript modules (with dependencies can be declared)
* The modules can have a common $moduleId "name", so it can be shared CMS-wide Ej jquery17, backbone, underscore, etc.
* If multiples modules with the same name are defined, it wins the last one.

https://groups.google.com/forum/?fromgroups#!topic/joomla-dev-cms/s2Wqo7eNKfo

	/**
	 * Adds a linked javascript module to the page.
	 *
	 * Example:
	 *
	 * $doc->addJavascriptModule('mediamanager', 'media/media/js/mediamanager.js');
	 * $doc->addJavascriptModule('installation', 'installation/template/js/installation.js', array('mediamanager'));
	 *
	 * Reference: Why AMD? http://requirejs.org/docs/whyamd.html
	 *
	 * @param   string   $moduleId      Value of module identication in the module loader.
	 * @param   string   $url           URL to the linked script
	 * @param   array    $dependencies  Array of module dependencies
	 *
	 * @return  JDocument instance of $this to allow chaining
	 *
	 * @since   11.1
	 */
	public function addJavascriptModule($moduleId, $url, $dependencies = array())