Add EALSTM

[gabrieltseng]

Adds an entity-aware LSTM, as described here: https://github.com/kratzert/ealstm_regional_modeling

Most of the code is just copied from the EALSTM described there, and fitted to our current RNN model.

Currently, the static data is the latlon data, but this should be updated to include landcover, and eventually topographical data.

[gabrieltseng]

TODO: add mean values

[gabrieltseng]

Added mean values. Specifically:

• Mean monthly values: these are (optionally) added to the current array
• Mean yearly values: these are (optionally) passed as an additional argument to the models. Different models deal with them differently.

[gabrieltseng]

Added standard deviations too