clean-up the vanilla biometrics pipeline API

bob/bio/base/config/examples/lda_atnt_legacy.py

bob/bio/base/config/examples/lda_atnt_legacy_all_legacy.py

bob/bio/base/config/examples/pca_atnt.py

bob/bio/base/config/examples/pca_atnt_legacy.py

bob/bio/base/config/examples/pca_mobio-male.py

bob/bio/base/mixins/__init__.py

bob/bio/base/mixins/legacy.py

...bio/base/pipelines/vanilla_biometrics/abstract_classes.py

bob/bio/base/pipelines/vanilla_biometrics/implemented.py

bob/bio/base/pipelines/vanilla_biometrics/legacy.py

bob/bio/base/pipelines/vanilla_biometrics/mixins.py

bob/bio/base/pipelines/vanilla_biometrics/pipeline.py

bob/bio/base/script/vanilla_biometrics.py

bob/bio/base/test/test_transformers.py

bob/bio/base/test/test_vanilla_biometrics.py

bob/bio/base/transformers/__init__.py

bob/bio/base/transformers/linearize.py

bob/bio/base/transformers/pca.py