Hi Xenia,

Below is a basic example that creates a panel with one row per list, displaying lists from multiple containers. The appearance of the panel could be modified pretty easily, and I hope this can provide a template to create your webpart. Let me know if you have any questions.

<script type="text/javascript">

Ext.onReady(function(){
    var allLists = [];
    var multi = new LABKEY.MultiRequest();

    var config = {
        schemaName: 'lists',
        includeUserQueries: false,
        success: function(result){
            if(result.queries.length)
                allLists = allLists.concat(result.queries);
        },
        error: function(response){
            console.log('There was an error');
            console.log(response);
        }
    };

    //identify the parent path using URL. this isnt fool-proof, since the current user might not have read permission in that container.
    // would also hard-code this path in your code, depending on your usage.
    var containerArray = LABKEY.ActionURL.getContainer().split('/');
    var parentPath = containerArray.slice(0, containerArray.length -1).join('/') || '/'; //default to root

    //add one AJAX request per container. the config is otherwise shared between then. also make sure we dont modify the original config object
    var containers = [LABKEY.ActionURL.getContainer(), parentPath]
    Ext.each(containers, function(c){
        multi.add(LABKEY.Query.getQueries, Ext.apply({containerPath: c}, config));
    }, this);

    //send multi-request, so we have since a callback when both are complete
    multi.send(function(){
        allLists = allLists.sort(function(a, b){return a.name > b.name ? 1 : (a.name < b.name ? -1 : 0);});

        //aesthetics could probably be improved on this panel
        //you could also choose to group these lists by container, rather than mingle them as this example does
        var config = {
            xtype: 'panel',
            title: 'Lists', //remove title and set border=false to hide the outer part of this panel and make it look more like the normal list webpart
            border: true,
            bodyStyle: 'padding: 5px;',
            defaults: {
                border: false
            },
            items: []

        };

        Ext.each(allLists, function(list){
            config.items.push({
                html: '<a href="' + list.viewDataUrl + '">' + list.name + '</a>'
            })
        }, this);


        new Ext.Panel(config).render('listDiv');
    }, this);
});

</script>
<div id="listDiv"></div>