Fix unified_data_layers.ipynb

[DahnJ]

Hi, I'm in the process of providing a streamlined version of unified_data_layers for H3-Pandas. This notebook is actually really useful for me, as it's a great non-trivial use case and informs what the API should look like! However, it was also broken, so I did my best to fix it without changing the functionality.

You can view the notebook in nbviewer

Commit messages have more info:

    Add dependencies to requirements
    
    rtree is required for spatial join
    xarray + rasterio for handling raster data without gdal_translate

    Refactor notebook, remove gdal_translate
    
    Problems solved
    - Outdated/broken code
    - Images displayed without running the code
    - No usage of gdal_translate, which didn't work in Binder
      (at least for me)

closes #5

[CLAassistant]

All committers have signed the CLA.

[DahnJ]

I have just noticed the issues in this repo regarding this notebook, I will check if this solves them, or whether I need to perform more changes.

edit: Okay, this closes #5. There's a valid point in #4 but I didn't want to change the actual functionality of the notebook, so I will keep it like it is. Plus it's not entirely clear to me whether the "smoothing" functions should function as a spatial moving average (as @GpoloVera suggests), or whether this is more of a "diffusion".

[ajfriend]

Thanks! Appreciate the fix!