Feature: various: remove support for pre-Pacemaker-1.0 CIB XML

Including:

• pacemaker-0.6, transitional-0.6, pacemaker-0.7, and pacemaker-1.1 DTDs/schemas
• Starting or performing rolling upgrades on clusters using validate-with set to one of those
• CTS support for pacemaker-1.1 schema
• <cib> tag's ignore_dtd attribute

Also, the API symbol CRM_DTD_DIRECTORY has been renamed to CRM_SCHEMA_DIRECTORY,
and all affected regression tests have been updated.