This PR:
* improves `Normalizer` class;
* adds a way to get detailed activations of a `TorchModel`;
* adds a tutorial on segmentation with `batchflow`, as well as ADE20k dataset;
* adds delayed imports mechanism and applies it to rarely-used libraries or ones with optional dependencies;
**Full Changelog**: https://github.com/analysiscenter/batchflow/compare/0.8.7...0.8.8