Add simple model training using Xarray

[jacobbieker]

This is linked to #18

This uses a very simple LSTM model to traing a predictor. The code is quite messy right now, so will need to clean it up first, but the model does learn something.

Todo:

• Clean up example generation, use datapipes
• Find out when most ELUC values are not-NaN
• Push updated dataset to HF with country mapping, and latlon coordinate
• Forecast both next year, and multiple years in future
• Expand model/Look at time series forecasting models

[jacobbieker]

1850 is the first time there is a non-NaN ELUC value