Extend meta tags for better search optimization and easier management

[skenow]

There are several key meta tags that are not included - especially those for localization

• geo.region
• geo.placename
• geo.position
• ICBM

These can be added directly to a theme, along with their values, but it isn't an easy thing for most people to do.

In addition, there are other meta tags, like open graph, that are key for social sharing.

We could take a simple approach and just add these to the meta preferences we have, or we could rewrite and add a separate class and table to allow site admins to add their own definitions.