Default value setting issues

[Andy0570]

Default value initialization

Default value of rowHighlightColor should set as ScrollStack.defaultRowHighlightColor.

ScrollStackRow.swift line 83:

    /// Row highlight color.
    open var rowHighlightColor = ScrollStack.defaultRowColor
    
    /// Row background color.
    open var rowBackgroundColor = ScrollStack.defaultRowHighlightColor {
        didSet {
            backgroundColor = rowBackgroundColor
        }
    }