Replace old advanced search form with new skeleton.

Add:
    static/js/index.js
        -Add header comments to existing search-group manipulation functions.

    static/sass/index.sass
        -Remove style rules for the old advanced search form.

    templates/index.html
        -Add element tree for new search form.
Style the sidebar; prepare for CSS onclick.

Add:
    static/sass/index.sass
        -Style `div#sidebar` contents.
Add checkbox-hack menu selection transitions.

Add:
    templates/index.html, static/sass/index.sass
        -Add pure CSS styling for "clicked" buttons, using the checkbox hack.
Add `add-group` button, style input fields.

Add:
    templates/index.html, static/sass/index.sass
        -Add element tree for a sample input field.
        -Style input fields such that labels are aligned.
        -Add and style the `add-group` button.
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.
Add search-group selection/removal.

Add:
    static/js/index.js
        -Add ability to select an existing search group to edit.
        -Add ability to remove search groups with a button.

    static/sass/index.sass
        -Add styling for `div#header`, which contains the titles of both columns
        ("fields" and "search groups") in the advanced search form.
Migrate search-form code to new file.

Add:
    static/js/(index > index.advanced-search-form).js
        -Migrate code relevant to the advanced search form to its own file.
        -Group global-scope function calls into wrapper functions executed on
        definition.
        -Add datepicker to new form's input fields.
Add query string assembly.

Add:
    static/js/index.advanced-search-form.js
        -Add `assembleQuery()`, which constructs a query string from the
        contents of the fields of the advanced search form's search groups.
Complete query assembly; add autocomplete menu.

Add:
    static/js/index.advanced-search-form.js, static/sass/index.sass,
    static/css/lib/jqueryui.custom.min.css
        -Add `jQuery UI` autocompletion menu to the advanced-search form's
        language input field, to replace `twitter typeahead` (which was
        incompatible with the new form's style rules).

    static/js/index.advanced-search-form.js
        -Add regex field specifier to query string.
Add advanced-query live update. Clean up.

Add:
    templates/index.html, static/js/index.advanced-search-form.js
        -Remove commented-out code, `testQueryStringGeneration()`, etc.; prepare
        for merging into `develop`.

    static/js/advanced-search-form.js
        -Perform a live update of the main query bar with a user's inputs in the
        advanced search form.