Improvements to CNNWhale class
This merge request adds:
- a unit test of the class constructor
- automatic detection of image size (shape) in the constructor
- asserts that data passed to the constructor are 'sane'
- a unit test that checks that the network can be trained with a very simple dataset
The last unit test is currently failing because the hard-coded dimensions of the network do not match those of the images in the simple dataset (which are 2x2 pixels). I suggest that we merge this into enh/nn/CNNWhale-make_network-structure-more-flexible and continue work on that branch