refreshes the header label
webix.ui({
container:"layout_div",
view:"accordion",
cols:[
{ header:"col 1", id:"a1", body:"content 1"},
{ header:"col 2", id:"a2", body:"content 2"}
]
});
$$("a1").define("header","new header");
$$("a1").refresh(); // header:'col1' -> header:'new header'