Application code infrastructure: base model, data module

[oleschwen]

Following #11, base models for classification and data modules for image datasets are duplicated in application/jobs/3dcnn_ptl and application/jobs/minimal_training_test. They could be extracted as some sort of "infrastructure" for application code using pytorch, CNNs, and image data; scope to be clarified a bit more (e.g., beyond CNNs, beyond classification?), if we consider this useful.