DNS additions

Add SSHFP record (closes #1594 (closed)), Add DNAME record (closes #1848 (closed)), get DNS templates by API (closes #3635 (closed)), Fix page width for user list slave zones (#5637 (closed)), Fix records page width (#5580 (closed)), fix DMARC checkbox (#4592 (closed)), display zone serial (read only) (Implements part of #2732 (closed))