Calculate receptive field for the models

[jakubczakon]

We may be training on too large images. Go through:

• https://medium.com/mlreview/a-guide-to-receptive-field-arithmetic-for-convolutional-neural-networks-e0f514068807
• https://arxiv.org/abs/1701.04128

Decide whether we are training on correct size images:

• Mayby smaller crops are enough in which case faster training is possible