This is a long MR with the following features:

• Proper checkpointing of scores (BioAlgCheckpointWrapper). Still in pickle, though
• Moved the score-writer outside of the VanillaBiometricsPipeline
• Simplified the scoring by BioAlgorithm. Also made once SampleSet, dump one score.
• Implemented a new pipeline that does Z, T and ZT score normalizations. Also created wrappers for Checkpointing and Dask this pipeline. Such pipeline has to wrap a VanillaBiometricsPipeline to work.
• Adapted the CLI command, bob pipelines vanilla-biometrics to work with ZNorm. Now, if you want to ztnorm a pipeline, just do bob pipelines vanilla-biometrics --ztnorm

Don't know if someone is willing to review this one.