[WIP] Add an embedding layer for the months

[gabrieltseng]

As per Yasser's comments, replaces the one hot encoding with an embedding.

~Currently, the size of the embedding is fixed at 12, but if this works well this could become an additional argument.~ The size of the embedding is an additional argument - if None is passed, the prediction month isn't passed to the model.

Also, removes the EALSTM cell written using nn.Modules, since the original one works fine with shap.

[tommylees112]

@gabrieltseng is this still good to merge?