Add GPT visualizations

[catherinesyeh]

• [x] rerun code to generate umap/tsne coordinates for GPT
  • [x] 2d
  • [x] 3d
• [x] recompute other info (e.g., attention)
• [x] add to attention-viz

[catherinesyeh]

• [x] should there be option to switch between gpt & bert?
  • if yes, should we pre-compute everything, or just load when user decides to switch between them?