Weeknumbers

Added functionality to display week numbers in date picker
Settings for to display week number  showWeekNumber : true  
I meant that you should move the `function () { ... }` into a named function so that it would be easier to read the complete line.

```javascript
var firstItemWeekNumber = function () {
    return [
        settings.week,
        settings.klass.weekNumbers,
        'scope=col'
    ];
};
```
```javascript
firstItem : settings.showWeekNumber ? firstItemWeekNumber : false
```