Support text attributes for LabelSegment

[ctwdtw]

Adding two properties normalAttributes, and selectedAttributes for LabelSegment,
so that it can display, for example, underlined text when being selected.

usage:

        let attr = [NSAttributedString.Key.underlineStyle: 1]
        control3.segments = LabelSegment.segments(
            withTitles: ["One", "Two", "Three", "Four", "Five"],
            normalFont: .systemFont(ofSize: 14.0),
            normalTextColor: UIColor(red: 0.15, green: 0.39, blue: 0.96, alpha: 0.9),
            selectedFont: .systemFont(ofSize: 14.0),
            selectedTextColor: UIColor(red: 0.16, green: 0.40, blue: 0.96, alpha: 1.00),
            selectedAttributes: attr
        )