Platform-specific icons, prices and authors

Hi,
First of all, thanks a lot for this useful library!

I did some minor changes to allow providing platform-specific values for the price and the icon. My project also needed to handle different values for authors. So I've added 3 new options, that fallback to the single value.
```javascript
    $.smartbanner.defaults = {
        author: null,
        authors: {'ios': null, 'android': null}, // Similar to above author, platform-specific
        price: 'FREE',
        prices: {'ios': null, 'android': null}, // Similar to above price, platform-specific
        icon: null,
        icons: {'ios': null, 'android': null}, // Similar to above icon, platform-specific
    }
```
Tried to do as little code changes as possible!

thanks,
mudar