ERRAI-736: Provide an ErraiBus WebSocket endpoint for WildFly/Undertow

3 new Maven modules:

- errai-bus-jsr356-websocket-parent: Parent for the concrete modules
- errai-bus-jsr356-websocket-non-jee: JSR-356 implementation for non JEE environments
- errai-bus-jsr356-websocket-cdi-weld: Extension for the errai-bus-jsr356-websocket-non-jee which enable CDI and provide builtin Request, Session and Conversation scopes

- There is additional a filter interface, that can be used to solve custom tasks before each message processing starts

- Negotiation extracted from org.jboss.errai.bus.server.servlet.JBossAS7WebSocketServlet into org.jboss.errai.bus.server.servlet.websocket.NegotiationHandler which is placed in errai-bus Maven module to avoid dependency to the errai-bus-jboss7-websocket Maven module from the other websocket modules.

- changed the default value of the context-init param "websocket-path-element" to "in.erraiBusWS". So this parameter is optional in the existing websocket modules and in the jsr-356 ones this can be omitted.

- Updated to documentation under errai-docs/src/main/asciidoc/reference.asciidoc. I dont knwo asciidoc before, so i hope its okay ;). Is there another place where the documentation should be updated?

Greez
Michel