move schema files to etc/ and modify makefile to install them into $(datadir)

	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

etc/Makefile

@@ -1,4 +1,4 @@
-ETCDIRS = styles
+ETCDIRS = styles schema
 -include local.mk	# optional local customization
 
 .NOTPARALLEL:	# always run this make serially