Test for 18.7.2. Update node properties
Test for 18.7.3. Get properties for node
Comment explaining absence of test for 18.7.4. Property values can not be null
Comment explaining absence of test for 18.7.5. Property values can not be nested
Test for 18.7.6. Delete all properties from node
Test for 18.7.7. Delete a named property from a node
Remove last big test from neo4j_test.go, it having been replaced with many
small tests in node_test.go.
Move emptyProps from tests to be exported EmptyProps in entity.go - probably
generally useful, not just for tests.