WebSocket endpoint should allow null path

Currently the endpoint is only available via ws://host:port/ws/

It will now also be available via ws://host:port/ws

(note the lack of the trailing slash).

URLs without trailing slash seem to be the standard for BOSH and WebSockets and are also used by XEP-0156.

This commit increases interoperability.

https://github.com/igniterealtime/Openfire/pull/1000