Add/expose random seed in LearningPipeline to get deterministic results

[GalOshri]

It is important to be able to set a random seed for ML experiments so the results are reproducible. Add random seed to LearningPipeline (or elsewhere) to ensure a full experiment is deterministic.

[markusweimer]

Which of those variants do you prefer?

  // Variant 1: Constructor
  var p = new LearningPipeline(seed:1234);

  // Variant 2: Property
  p.seed = 1234;

  // Variant 3: Parameter to .Train()
  var m = p.Train(seed:1234);

[zeahmed]

I'll prefer

// Variant 3: Parameter to .Train()
var m = p.Train(seed:1234);

[TomFinley]

Seriously, enough is enough I think. Let's just expose IHostEnvironment. That's our mechanism to solve this and other problems, it's worked well for years doing exactly this among all its other functions.

[shauheen]

With a few PRs already merged as well as the proposed #371 , this issue can now be closed.