Since: BlackBerry 10.3.0
A class that represents the different modes of a Header.
The supported modes of a Header include Default, Plain, and Interactive.
The Default mode selects the mode automatically based on whether there's a slot connected to the onClicked() signal or not.
In Plain mode, the header supports a title and a subtitle.
In Interactive mode, the header supports a title, a subtitle, and a clickable button.