Added MultiNetPatchClassifier extractor and utils, temp fix in LightCNN9

Extractor allowing to pass multiple patches (for example, face regions) through multiple, or single, networks (autoencoders, or any other DNN).

TODO: once LightCNN9 issue is fixed in bob.learn.pytorch, undo the temp fix in LightCNN9 class.

TODO: enable unit tests for LightCNN9, when above fixed.