Refactor code and integrate command-line config

[alexkrz]

The idea would be to integrate jsonargparse functionaility as done in the Pytorch Lightning CLI.
Documentation on jsonargparse is here: https://jsonargparse.readthedocs.io/en/stable/

We should stop reading values directly from the config dictionary.
Instead the code in tile_generator.py should be split into several functional parts with clear APIs.

Also we should think about which arguments are the most relevant and which others we should by now integrate as default.