Added watcher on total items

I had some issues when I was updating the "total" attribute.
Basically the directive didn't re-build itself, because you were watching only the "page" change.

All I did was adding the watcher on the total too.

With Angular 1.3 we can do a group watch too:

```javascript
     $scope.$watchGroup(['page', 'total'], function(newValues, oldValues, scope) {
  // newValues array contains the current values of the watch expressions
  // with the indexes matching those of the watchExpression array
  // i.e.
  // newValues[0] -> scope.foo 
  // and 
  // newValues[1] -> scope.bar 
});
```