Add examples on how to leverage la.functional_samples()

[wiseodd]

Now that #243 is merged, it's useful to have some examples of how to leverage la.functional_samples() in practical applications. My plan is to create two examples (can be merged as one):

1. Thompson sampling: la.functional_samples(pred_type=PredType.NN), citing https://proceedings.mlr.press/v70/hernandez-lobato17a.html
2. General MC-acquisition function: la.functional_samples(pred_type=PredType.GLM) (or NN), citing https://arxiv.org/abs/1712.00424