Add two new aesthetic embeddings

[vicgalle]

This PR adds the following new aesthetic embeddings:

• [x] Fantasy: created from https://huggingface.co/datasets/ChristophSchuhmann/improved_aesthetics_6.5plus by filtering only the images with word "fantasy" in the caption. The top 2000 images by score are selected for the embedding.
• [x] Flowers & plants: created from https://huggingface.co/datasets/ChristophSchuhmann/improved_aesthetics_6.5plus by filtering only the images with word "plant", "flower", "floral", "vegetation" or "garden" in the caption. The top 2000 images by score are selected for the embedding.

Some examples:

• Without aesthetic embedding:
• With fantasy.pt:
• Without aesthetic embedding:
• With flower_plant.pt:

TODO:

• [x] Update README