ws: split zone get/list into it's own function
introduce DNSBackend::createDomain

Includes an implementation for GSQLBackend.
allow reuse of DomainInfo::kind enum
introduce new setMaster/setKind functions
implement setMaster/setKind in GSQLBackend
expose create zone in JSON webserver
introduce DNSBackend::deleteDomain
implement deleteDomain in GSQLBackend
expose zone DELETE in JSON webserver
Merge pull request #1036 from zeha/create-domain

Internal and HTTP API for creating and deleting domains