Add carousel to front page

This commit adds the Foundation Orbit carousel to the front page.
The images and caption text are included in the index.html file:

/themes/hugo-theme-digikam/layouts/index.html

Follow the same convention to add another .orbit-slide <li> element
and the associated <figcaption> text.

Don't forget to add another <button> below it, increment the
'data-slide="X"' value and add appropriate text for screen readers.

Gilles included text in /static/img/carousel/info.txt. I've made
some minor grammatical changes to that file.