Adds element to typeahead callback function arguments

Offers a way to use the same callback function for multiple elements.

Usage example:

View
```html
<input name="brands" type="text" bs-typeahead="typeaheadFn" />
<input name="models" type="text" bs-typeahead="typeaheadFn" />
```

Controller
```javascript
$scope.brands = {"brands":[{"label":"ALFA ROMEO"},{"label":"AUDI"}]};
$scope.models = {"models":[{"label":"Mito"},{"label":"A 1"}]};

$scope.typeaheadFn = function(query, element) {
    return $.map($scope[element[0].name], function(e) {
        return e.label;
    });
}
```