Move adv-search form buttons. Close #65.

Add:
        templates/index.html, static/sass/index.sass
                -Move the "add group" and "remove group" buttons inside the
                advanced-search form to a different location.

        static/img/index/
                -Following convention established by the "about" page, all
                page-specific images should be located in a subdirectory of
                `static/img/` named after the page. Add `index` dir.