(v1.0) Re-organized ExcelBuilderAction.php.twig

Added  a ```getValueForCell``` protected function so that extending the values format for the cells will be easier.

For instance if we need to format the value of a field which we know it's a currency, we can easily extends this method and add those special cases. E.g.:
```php
protected function getValueForCell($field, $rowData)
{
    switch($field) {
        case 'price':
        case 'productionCost':
            $getter = 'get'.ucfirst($field);
            $data = number_format($rowData->$getter(), 2, ',', '.');
            break;
        default:
            $data = parent::getValueForCell($field, $rowData);
            break;
    }
    return $data;
}
```

I don't know if this is the best example, but this can also be used to render boolean field with some text other than ```TRUE/FALSE```.
@Restless-ET maybe instead of *"one method to format them all"* something like this?

```php
<?php

protected function createExcelData(\PhpExcel_Worksheet $sheet)
{
    $row = 2;
    $results = $this->getResults();
    foreach($results as $rowData) {
        {%- set column = 0 -%}
        {%- for builder_column in builder.columns %}
            if (method_exists($this, 'format{{ column.name|classify }}Value') {
                $data = $this->format{{ column.name|classify }}Value($rowData);
            } else {
                $data = $rowData;
            }

            $sheet->setCellValueByColumnAndRow({{ column }}, $row, $data);
            {% set column = column + 1 %}
        {%- endfor %}
        $row++;
    }
}
```

This way, for column "name", if you add (in your `ExcelController.php`) a method `formatNameValue`, it will be used to format the value for this column. Otherwise raw value will be used.