This adds initial support for accounts a concept meant to signify a customer, a department or any other entity that somehow owns or manages one or more domains.
The purpose is to be able to assign an account to any number of domains, making it easy to track who owns or manages a domain, significantly improving manageability in setups with a large number of domains.
An account consists of a mandatory, unique `name` and optional `description`, `contact` name and `mail` address. The account `name` is stripped of spaces and symbols, and lower cased before getting stored in the database and in PowerDNS, to help ensure some type of predictability and uniqueness in the database.
The term *account* is actually taken from the PowerDNS database, where the `domains.account` column is used to store the account relationship, in in the form of the account `name`.
The link to a domain in PowerDNS-Admin is done through the `domain.account_id` FOREIGN KEY, that is linked to the `account.id` PRIMARY KEY.
(cherry picked from commits 4e95f33dfb0676d1c401a033c28bca3be7d6ec26, da0d596bd019a339549e2c59630a8fdee65d0e22, 7f06e6aaf4fd8011c784f24b7bbbba5f52aef319, 1c624dad8749024033d1d15dd6242ca52b39f135)
The options for SOA-EDIT-API included was actually the options used for SOA-EDIT, which is a very different beast.
Those options have been swapped out for the options allowed in SOA-EDIT-API and SOA-EDIT-DNSUPDATE.
Accept IdP EntityID to use when metadata contains more than one IdP.
Allow specifying attribute names to get given name, surname, and email address.
Allow specifying NameIDFormat to request.
Allow specifying whether to get username from a named attribute, or NameID.
Allow getting administrator state from attribute.
