As a SM I want control over how my shared page appears on other websites (Metatag / Open Graph)

There are various established metatags that control how a page is displayed when shared to another website. Open Graph is propagated by Facebook (and also used by Google+ and other websites). Twitter has their own tags. If these tags are not used then the page will be crawled for an image to be used. As the logo is the first image on any page it usually is what's used but this is not always desirable.

Acceptance criteria

• As a site manager I want to be able to set a fallback image for all pages that is set as Open Graph and Twitter image
• I want to be able to enable the usage of hero images for content types that have these

Pages to look at:
- Homepage
- Content pages
- User profiles

Suggested implementation
Enabling the metatag module should provide enough control for most site builders. For sitemanagers this might be a little too complex so an alternative UI should be made that overwrites these specific Metatag defaults.