Add youtube video description to content

[swentel]

Adds YouTube media:description to content.

With the new flag in XRay, the iframe tag can also be preserved for direct playing in readers then, if wanted of course.

This is code for a test in XRay - the rss feed is the from your rss channel, located in a new dir www.youtube.com

youtube.rss.txt
(had to rename to .txt because it wouldn't upload otherwise)

  public function testYouTubeFeed() {
    $url = 'http://www.youtube.com/youtube.rss';
    $response = $this->parse(['url' => $url, 'expect' => 'feed']);

    $body = $response->getContent();
    $this->assertEquals(200, $response->getStatusCode());
    $result = json_decode($body);
    $data = $result->data;
    $this->assertNotEmpty($data->items[0]->content->text);
    $this->assertContains('The just-announced ATEM Mini Pro has some incredible new features', $data->items[0]->content->text);
  }
php```