Migrate HTML visualizations to Gradio Blocks

[gsarti]

🚀 Feature Request

~~Use the newly introduced PySvelte library and the Svelte framework to deduplicate HTML visualization from the main body of the library.~~

Update: Provided the new capabilities of Gradio v3.0 and the introduction of support for custom components with Gradio Blocks (using Svelte as frontend) and tabbed interfaces enabling multi-visualization widgets, Gradio becomes the most simple and interesting choice for Inseq visualizations.

[gsarti]

A possible visualization of saliency not relying on the entire matrix visualization might use either Ecco.js or gradio.HighlightedText