Provide description text for all file formatters

Right now we don't provide any description on file formatters that are provided by hook_file_formatter_info. There are quite a few that exist in manage file display and right now you have to turn them on to see how they work since we don't describe them.

Oembed does provide descriptions:

<?php
/**
 * Implements hook_file_formatter_info().
 */
function oembed_file_formatter_info() {
  $formatters['oembed'] = array(
    'label' => t('oEmbed'),
    'default settings' => array('width' => '560', 'height' => '340', 'wmode' => ''),
    'view callback' => 'oembed_file_formatter_view',
    'settings callback' => 'oembed_file_formatter_oembed_settings',
    'description' => t('All-purpose oEmbed formatter.'),
  );
  $formatters['oembed_thumbnail'] = array(
    'label' => t('oEmbed thumbnail'),
    'default settings' => array('width' => '180', 'height' => ''),
    'view callback' => 'oembed_file_formatter_view',
    'settings callback' => 'oembed_file_formatter_oembed_thumbnail_settings',
    'description' => t('oEmbed thumbnail media.'),
  );
  return $formatters;
}
?>