Simple OS and Device Detection

I saw on your road map that you wanted to be able to include simple OS and device detection.  This pull request does just that.

I tried to keep it very minimal to keep in the overall lightness of xui to begin with.

**Example:**  `x$.os.iphone` (would return a boolean)

**Devices:**
`x$.os.iphone`
`x$.os.ipod`
`x$.os.ipad`
`x$.os.android`
`x$.os.blackberry` _Will return true for webkit based Blackberry phones_
`x$.os.blackberryplaybook`
`x$.os.windowsphone`
`x$.os.kindlefire`
`x$.os.phone`
`x$.os.tablet`
`x$.os.desktop`
`x$.os.othermobile`