Browser plugins that display a form now require use of $form['actions']

For Media browser plugins that output a form, the use of $form['actions'] for all the submit buttons is required so that the fake cancel button can be properly added in the correct place.

Before:

function mymodule_media_browser_form($form, &$form_state) {
  ...
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
  );
  return $form;
}

After:

function mymodule_media_browser_form($form, &$form_state) {
  ...
  $form['actions'] = array('#type' => 'actions');
  $form['actions']['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
  );
  return $form;
}