etc/Makefile: add "schema" to $(ETCDIRS)
contrib/odt/etc/schema/od-manifest-schema-v1.2-cs01.rnc: move to etc/schema/od-manifest-schema-v1.2-cs01.rnc
contrib/odt/etc/schema/od-schema-v1.2-cs01.rnc: move to etc/schema/od-schema-v1.2-cs01.rn
contrib/odt/etc/schema/schemas.xml: move to etc/schema/schemas.xml