A tab container is a card-layout container with a tab bar and styled buttons.
Do not specify a `layout` for tab containers.

The buttons are configured via `header`

    activeIndex: 2,
    tabBarPosition: 'left', // top, right, bottom, left
    itemDefaults: { module: Button },
    items: [{
        header: {
            iconCls: 'fa fa-home',
            text: 'Tab 1'
        }
    }, {
        header: {
            iconCls: 'fa fa-play-circle',
            text: 'Tab 2'
        }
    }, {
        header: {
            iconCls: 'fa fa-bell',
            text: 'Tab 3'
        }
    }]
