[script.*] Change prediction to write dataset predictions on a subfolder named after the dataset name in the current run

[script.analyze] Issue warning if keys do not match on for second-annotator evaluations (should not happen, normally)

[script.evaluate] Fix second-annotator comparisons with a key-resemblance check; Add assertions in engine.evaluator to ensure proper comparisons

Cleanup model implementation

See merge request bob/bob.ip.binseg!13

[models,configs/models] Cleanup model implementation to re-use all backbones from torchvision; Simplify checkpointer; Remove own implementation of model_zoo; Implement normalization for torchvision-based backbones; Enables pytorch installation on osx

[engine.*trainer] Set non-blocking operation for CPU->GPU data transfers to make communication asynchronous