* add XSD element for nested router type * add tests on the matter * polishing for RouterParserTests JIRA: https://jira.springsource.org/browse/INT-2893 INT-2893: Polishing INT-2893: after rebasing to 3.0 XSD changes reverted from 2.2 and moved to 3.0 INT-2893 Polishing Factor out common elements; fixing missing documentation for `expression` within a `router` within a `chain`.