Use WP Blog meta for domain mapping

There is currently a core ticket to add a new table called [wp_blogmeta](
https://core.trac.wordpress.org/ticket/37923). This would be a network level shared table for the wp_blogs table. It is currently in development, as a feature plugin [here](https://github.com/stuttter/wp-blog-meta).

It would be great to use blogmeta in this drop-in once it is in core. It means that you would not have to create another table on installation. Also many of the core functions could be used in the CRUD process.