appendTo support for components

[cagataycivici]

AppendTo property of components such as dropdown, overlaypanel only support html elements like divs, we also need support for other components so that element can be appended to a panel or datatable.

<p-overlayPanel #op1 [appendTo]="dt">
        <img src="showcase/resources/demo/images/galleria/galleria1.jpg" alt="Galleria 1" />
    </p-overlayPanel>

<p-dataTable #dt