UIButton 子类：ALButton

ALButton 是 UIButton 的子类，添加了一些功能，减少 UIButton 自定义外观和行为的行数，并且添加了一些 Swfit 的优势。

三种初始化方式：

//- 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")