Moved Cache $content collection to Element

The Cache details only included all the Model & Controller level Caches

that is, it contained all Cache utilization until the `beforeRender()` callback

Now, it will also include all the Cache utilization during the render process (until this element is rendered)
which means it should get all Application Views/Helpers/Elements too.

(NOTE: the title of the tab will not be accurate with the extra details from View/Rendering)