Add ajax request feature

[igor-kremin]

Hello friend, I was looking through the web for the multi-select which can use input checkboxes as select items and what was most important to me is that the widget does not add any plates outside the select box with the selected items. As I want to use it in filter box which size is fixed. But I need to use an ajax request to the backend to access large amount of items.
So I did the update for your script:
the widget make request to the backend for the url specified in option ajaxUrl  Server response with the json object like 
{
    "results": [
        {
            "id": 138,
            "text": "4SEASONS"
        },
        {
            "id": 10453,
            "text": "ADIM PLASTIK"
        },
        {
            "id": 11196,
            "text": "ASAM"
        },
    ],
    "pagination": {
        "more": true
    }
}

The widget rebuilds all items except checked (all checked items left on the top of the list).Also I scrolls list results to the last selected item, what seems to be more usable for other items to select.