Add ability to not have images in meta data

[koppen]

With auto_display_meta_tags image tags are always generated, even if no images have been configured for a page, resulting in meta tags like:

<meta itemprop="image" content="https://example.com/images/" />
<meta name="twitter:image" content="https://example.com/images/" />
<meta property="og:image" content="https://example.com/images/" />

Those URLs don't resolve to actual images and are simply defaults/faulty.

With this change in place, those faulty meta tags aren't output.

[tiste]

Great!