NicMX compatibility

A bunch of features have been added, mainly due to the contribution of @jbarbede. php-epp2 should now be fully compatible with the epp interface of nic.mx :)

Full Changelog

Fixed

• some minor logical fixes and typos

Added

• Domain::setBillingContact: set billing contact while creating domains (thx @jbarbede)
• Domain::addBillingContact: add billing contact while updating domains (thx @jbarbede)
• Domain::removeBillingContact: remove billing contact while updating domains (thx @jbarbede)
• Client::login: add ability to passthrough svcExtensions via Client config (thx @jbarbede)
• Transfer: add query type operation
• NicMX Extension (thx @jbarbede)