UIButton 子類：ALButton

ALButton 是 UIButton 的子類，添加了一些功能，減少 UIButton 自定義外觀和行為的行數，并且添加了一些 Swfit 的優勢。

三種初始化方式：

//- 1. Full Initialization
let style = ALButton.ButtonStyle()
//-- set style
let myButton = ALButton(title: "Button Title", style: style, touchUpInsideHandler: {
    (sender ) in
    //-- Implement touch up inside event here
})
//- 2. Simple initialization with style:
var style = ALButton.ButtonStyle()
//-- set style
let myButton = ALButton(title: "Button Title", style: style)
//- 3. Short initialization
let myButton = ALButton(title: "Button Title")