Add similarity search of datasets in OpenML database

[MorrisNein]

We may add a similarity search that functions the following way:

1. Extract necessary metafeatures from a custom dataset (implement corresponding MetaFeaturesExtractor in #3 or in another PR)
2. Load the full OpenML datasets database
3. Find the N nearest datasets by DatasetsSimilarityAssessor
4. Load all evaluations for the closest datasets from OpenML datasets (implement corresponding ModelsLoader in #3). Filter out the best M models for each dataset
5. Provide a final report to the user