PHPPortlet should obtain servelt objects from a Factory

The PHPPortlet requires that HttpServletRequest, HttpServletResponse and ServletConfig be set as PortletRequest attribute with a specified key. But if we specify an interface called ServletObjectsFactory that has methods to return the above mentioned objects then we don't need to depend on any specific attribute. The implementation of the interface can be set in the portlet.xml as a context-init parameter, so that in the Portlet.init(), we can get the implementation. And in the code we can get the objects from the implementation.

Also presently PHPPortlet writes the output to HttpServletResponse.getWriter(), it should be written to RenderResponse.getWriter()