Fix blocky effect

[SarahAlidoost]

closes #17

This PR adds :

• a documentation on how to select the patch sizes, read this carefully when setting up training.

This PR fixes main things as:

• a bug in the optimization loop in the notebook, how loss is calculated
• a bug in the optimization loop in the notebook, how land mask is applying
• a bug in reshaping arrays inside the model
• a bug in the notebook in inference (prediction cell).

This PR also improves:

• the spatial refinemnet
• the dataset class to cover the whole input data
• disable overlapping data batches created by dataset because it affects the loss

Results:
Note: As can be seen in the final plots, there is not spatial artifacts. I also run the notebook on residuals in this branch. The results also are without artifacts.

Note: The notebooks in this PR can be run on local systems. If the input size or data patch size are changed, the model patch size and overlap should be adjusted accordingly.

[SarahAlidoost]

@meiertgrootes please also see the top comment when reviewing.