Anjelina,
I have recompiled the widget for 3.6 (attached zip file). You will not be able to use it with the web app builder so you will have to add the widget to the config file manually:
<widget label="Layers" right="10" bottom="10" preload="open"
icon="assets/images/Legend32.png"
config="widgets/TOCGroup/TOCGroupWidget.xml"
url="widgets/TOCGroup/TOCGroupWidget.swf"/>
then amend the widget config for your layers it should be pretty much self explainatry
Regards
Anthony