WIP: Implement CloudFlare support

Very early version. Please provide feedback.
Do you want support for this in poweradmin?

CloudFlare API documentation:
https://www.cloudflare.com/docs/host-api.html

We probably want to implement some sort of CloudFlare user management instead of the `$cloudflare_user_key` setting, but it works for now.

The new `records_meta` table can probably also be used to implement fancy ting like http redirects.

(Sorry bad english, it's not my native language.)