Add OG tags to journal's homepage

[marcbria]

Now the tags are added to the article page, but it would be nice to extend the plugin to add the same tags to the main journal page.

Ideally it would be nice to extend to the archive page, about pages, ads and all other pages.

In those cases, not having a clear page image to associate, I suggest using the logo and general journal data for the open graph tags.

Actually, all this is not something dramatic or essential (few things are ;-)), but it helps the promotion of the journal when publishers distribute the url of their publication all over the world.

Thanks so much AJ for the plugin and for sharing all your work so generously.