fix reset for single DropDown

[Batwam]

in relation to #80, see update to fix reset button for single DropDowns. The variables should have been arrays.

[Moon-0xff]

Ah! Now I get it. addDropDownList returns an array.

Another fix would be to return the first element of the array on addDropDown:

function addDropDown(group,settings,labelstring,options,labeltooltip,width=105){
        return addDropDownsList(group, [settings], labelstring, [options], labeltooltip,width)[0];
}

But I think your solution is better.

I'll merge this right away.