MONAI support

[brudfors]

This PR allows for use of the metrics in pairwise_measures.py to be used from MONAI, in particular it enables the use of a batch dimension and a smoothing parameter. Some small modifications have also been made in some places to make the code slightly more efficient (e.g, one-hot encode only once in MultiClassPairwiseMeasures.weighted_cohens_kappa , repeated computations removed from MultiClassPairwiseMeasures.normalised_expected_cost., etc). All unit tests pass, and the smoothing parameters is disabled by default; that is, the output of the metrics have not changed. With this PR integrated into the package, the wrapper on the MONAI side (for the pairwise metrics) should be easy to implement :)