Resamples the instances in order to achieve a uniform class distribution. If the class
distribution is already uniform, nothing is changed. In all other cases, this results in dropping
FIXME: This is currently optimized for memory consumption and might be slow for large feature
stores. If there is enough memory (at least 2x the size of the current feature store) a time
optimized version should simply create a new feature store that only holds the selected
instances. In the worst case, this would double memory consumption.