INT-3418: Prepare 4.1 VERSION

JIRA: https://jira.spring.io/browse/INT-3418

* Create 4.1 XSD
* Clean up Docs for 4.1
* Prepare WebSocket module
* Add Reactor dependency
* Remove Eclipse and SNV artifacts

Phase #1: prepare

Conflicts:
	gradle.properties
INT-3418: xsd-1.0 -> 2.0
INT-3418: xsd-2.0 -> 2.1
INT-3418: xsd-2.1 -> 2.2
INT-3418: xsd-2.2 -> 3.0
INT-3418: xsd-3.0 -> 4.0
INT-3418: xsd-4.0 -> 4.1
INT-3418: Final Phase: Cleanup

INT-3418: use versioned XSDs for XSD import
INT-3431: Fix `RecipientListRouter.onInit()`

JIRA: https://jira.spring.io/browse/INT-3431

The introduced `late channel resolution by name` via https://jira.spring.io/browse/INT-3324
has lost `onInit()` propagation from `RecipientListRouter.onInit()`