Complete the websocket ramp set

[Licenser]

Describe the problem you are trying to solve

At the moment we only have half the WebSocket ramps.

we have a WebSocket server as an onramp and a WebSocket client as an offramp. To complete the set we should add a WebSocket client onramp and a WebSocket server offramp.

Describe the solution you'd like

The WebSocket client onramp would connect to a given WebSocket server and publish all messages from that server into the connected pipelines.

The WebSocket server offramp would allow clients to connect and send the events it receives to all clients that are connected at the time of arrival.

[Licenser]

This goes hand in hand with linked transports ( #64 ) :) tossing it to @anupdhml

[mfelsche]

FTR this should be solved when we implement Connectors: tremor-rs/tremor-rfcs#32

[Licenser]

This is done with connectors