add virtual stream

[Even Solbraa]

Is your feature request related to a problem? Please describe.
Virtual stream is a useful unit operation needed in various process simulation cases

Describe the solution you'd like

VirtualStream newStream = new VirtualStream(feedstream)

VirtualStream

run(){
outStream = feedStream.clone();
}

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.