Allow another modules to alter modal window options.

Hi, first of all thx for this great module!

I'm new to ctools modals and have a task to theme modal, so I've made research how to override modal options.
Here possible solutions:

• Using Drupal.theme.prototype.CToolsModalDialog but this will override all ctools modals
• Using drupal_add_js
  

  drupal_add_js(array(
    'ctools-ajax-register-style' => array(
      'modalTheme' => 'custom_theme'
      'closeImage' => theme('image', array(
        'path' => drupal_get_path('theme', 'mytheme') . ('/img/modal_close.png'),
        'title' => t('Close window'),
        'alt' => t('Close window'),
      )),
  )), 'setting');
  

  + modalTheme setting. This is more elegant.

But, when custom/contrib theme/module has soft dependency to yours, first one do wasted drupal_add_js calling or prototype declaring. Сertainly developers can add module_exists/fuction_exists for additional check or even module dependency in .info.

I propose to add alter hook via drupal_alter() that allows another modules to act with modal options variable.
Patch icluded below.

If this solution is excess, please, close issue.