Change selectors and add early php function markup draft

Javascript now tagets DT tags instead of LI. Because Wordpress uses
DT's by default for galleries.

Changed the element child counter to count only DT's, as there will be
both DT's and their captions DD's now.

Changed the JS file's selectors to account for the items being wrapped
by their semantic dl inside the slideshow ID.

Add some markup to the plugin's default slideshow function.