Add ECOGEN embedding and generative

[sammlapp]

ECOGEN is a self-supervised (VQ-VAE architecture) encoder-decoder trained on xeno canto. It was created for generation of new samples by perturbing the feature space (called the code book), but could also serve as an effective embedding model using only the encoder half. The model and code are open-source, though I haven't successfully installed the repo in a python package yet (see ixobert/birds-generation#7)