Menu scroll strategy

Pursuant to: http://forums.enyojs.com/discussion/1353/always-show-scrollbar-on-picker

I have added the ability to select a scroll strategy when creating a menu.  The default remains TouchScrollStrategy, but for desktop that strategy leaves something to be desired.  Using ScrollStrategy instead will present a scrollbar on the menu.

Let me know if this doesn't fit with your vision for implementation.

Also, I took the liberty of fixing a whitespace issue in Picker.js.  Sorry to combine that with this pull request.

Example usage:
```
  {kind: "onyx.Picker", 
    name: "myPicker", 
    onSelect: "pickerChanged", 
    scrollStrategyKind: "ScrollStrategy", 
    components: [
      {content: "15 minutes", active: true},
      {content: "30 minutes"},
      {content: "60 minutes"}
    ]
  }
```