fix: add sys.nodes and sys.cluster expressions to UnassignedShardsReferenceResolver

this way a query like  select sys.nodes.name, * from sys.shards
also works if there are unassigned shards.
added routing column example using compound primary keys
Merge pull request #711 from crate/l/add-routing-col-example

added routing column example using compound primary keys
prepare release 0.35.6
Merge tag '0.35.6'

Tag release for revision 0.35.6

Conflicts:
	CHANGES.txt
	core/src/main/java/io/crate/Version.java
	sql/src/main/java/io/crate/operation/reference/sys/shard/unassigned/UnassignedShardsReferenceResolver.java
	sql/src/test/java/io/crate/integrationtests/TransportSQLActionSingleNodeTest.java
Merge branch 'master' of github.com:crate/crate