Allow all Google Chart options

Hello,

here's a patch that allows to set all options available for Google Charts (i.e. for Line Chart). There's currently another issue (#1809850: Provide more ability to override chart options) requesting more control over charts as well. However, I create a new issue since the other issue contains patches for Highchart - I don't want to mix them.

What this patch does:
Most important thing: it doesn't break current implementations.
You are now able to add an array to the $options array which is passed to the theme function. This array contains all the options you like. So the $options array passed to the visualization theme could look like this:

$options = array(
    'title' => '',
    'fields' => array(
      'date' => array(
        'label' => t('Date'),
      ),
      'count' => array(
        'enabled' => TRUE,
        'label' => t('Sold Products'),
      ),
    ),
    'xAxis' => array(
      'labelField' => 'date',
    ),
    'data' => $data,
    'type' => 'line',
    'chart_options' => array(
      'backgroundColor' => '#E0E0E0',
      'hAxis' => array(
        'textPosition' => 'in',
      ),
    )
  );

Hope this will be reviewed and committed soon as I have heavy need for this ;)

Kind regards,
haggins