[js] remove 3.9 bw compat (where apparently unused) - cubicweb.ajax.js - loadxhtml: form.callback support removal - removal of top-level functions: preprocessAjaxLoad, reloadBox, replacePageChunk, loadxhtml - cubicweb.compat.js: - map is undeprecated (jquery.map being not an acceptable replacement) - removal of noop, contains, findValue, filter, addElementClass, removeElementClass, hasElementClass, KEYS mapping - htmlhelpers.js: use non-deprecated functions cw.urlEncode - cubicweb.js: - removal of startsWith and endsWith monkeypatches - note deprecated but still used stuff (for action) - test_utils.js: use cw.utils.sliceList instead of global function Closes #2782004.

$(document).ready(function() {
    $('a.rhythm').click(function (event){
        $('div#pageContent').toggleClass('rhythm_bg');
        $('div#page').toggleClass('rhythm_bg');
        event.preventDefault();
    });
});