improved websocket session handling
adapted handling of connect messages: each WoN node has its own copy

when a message is received, it is assigned a new messageURI and the content is copied, so that it can consistently be served by the WoN node as linked data
Merge branch 'devel' into feat-accept-connect

Conflicts:
	webofneeds/won-owner-webapp/src/main/java/won/owner/web/websocket/WonWebSocketHandler.java
	webofneeds/won-owner/src/main/java/won/owner/service/impl/OwnerApplicationService.java
merged
merged