Add ability to add input fields/groups.

Add:
    static/js/index.js
        -Add callback functions to the buttons/checkboxes in `#sidebar`, which
        allow the user to add new search groups, and to add input fields to the
        currently selected search group.

Rem:
    static/js/index.js
        -Remove obsolete functions which allowed the creation/deletion of search
        groups in the old form.