Migrate GlotPress standalone users and usermeta tables about glotpress

[gilbitron]

👍

[toolstack]

I don't know if this is even necessary, GP has never had a 1.0 release so anyone who's installed it can expect breaking changes and this could fall in to that category. Especially since most people who would be interested in it probably already run GP using the WP users table :)

[JRGould]

This seems like functionality that should go into a plugin as it will probably be used/useful for only a short time after the GlotPress plugin is released. After that, it will mostly just be cruft that needs to be maintained indefinitely or have a committee vote to remove it.

[bradt]

Punted as per https://wordpress.slack.com/archives/glotpress/p1443706375001022.

[toolstack]

Closing as won't fix as we're well beyond this now :)