expose input_shape and add config tests

[quantumjot]

• [x] expose input_shape as a command line argument
• [x] add tests to check that arguments are correctly passed to models
• [ ] add verification that input_shape is reasonable

Closes #9, #27

[quantumjot]

Hi @KristinaUlicna - this branch add support for different input shapes, take a look and see if it works for you!

python run_training.py --input_shape=(128, 128, 1)