Train convolutional neural networks with Keras API

This new release is characterized by the transition from the TensorFlow library to the Keras library so as to train neural networks and predict image labels.

Additionally, the code has been structured in a production-like purpose:

• the program modules have been moved to a deeposlandia repository;
• a tests repository contains a bunch of tests that guarantee the code validity;
• a setup.py file summarizes the project description and target. Some complements may arise in order to publish the project on Pypi.