Add unit test based on the example data/model

[eduardojdiniz]

It would be great to have unit testing (a git hook, maybe?) based on the age predictions for the two sample T1 images using the example model (or even, all the supplied models, although that may slow down things).

[eduardojdiniz]

A good start point is to write a script to go over all models and store in a single file all the age predictions for the two sample T1 images. The values can later be compared with the known ground truth.