additional tensorboard logs for batches

[hstojic]

currently we have histograms of query points when it comes to batch BO that are useful for checking the diversity, that all seems to work fine - there are two more that would be quite useful:

1. histogram of pairwise distances between query points - its easy to compute pairwise euclidean distances with Scipy's pdist and then use logging.histogram
2. pairplot with individual scatterplots for each input dimension and model predicted output - this one is a bit more work and we would need to use image summary