LP1944755 Add ability to embed carousels on external pages

LP1944755 Add ability to embed carousels on external pages

This displays carousels on an otherwise blank page, allowing
libraries to very easily embed them on their web sites using iframes.

Example iframe code:
<iframe src="(my opac domain)/eg/opac/carousel?carousel_loc=4" title="Carousel"
width="80%" height="500px;" frameborder="0"></iframe>

The base_simple code could also be used by other future features
that are driven by Evergreen but that shouldn't display the headers and
footers.

Signed-off-by: Terran McCanna <tmccanna@georgialibraries.org>