LPS-30099 Embedded system portlets' css not getting included

Hi Ray,

This is a fix I'm planning to send you for a while now. The original problem is that the LayoutTypePortlet.getAllPortlets filters out the embedded system portlets and when we are getting what css and JS we are about to include on a page, the staging bar is an embedded system portlet thus it's css won't be included on the page.

So I've decided to refactor how we are getting back the portlets. I've tried to simplify and improve the way we are doing this, be adding a mechanism to include or not include the portlets associated with a layout. Now we have control over this, so we can specify in every case what kinds of portlets do we want from a layout.

I also wrote javadocs to explain what method and constant is for what, and I've extended the test class for the LayoutTypePortlet.

Thanks,

Máté