fixed favicon issue

[abidlabs]

We had dropped support for favicons at some point. This implements it again. Closes: #1036

Sample code to test:

import gradio as gr

gr.Interface(
    fn=lambda x:x,
    inputs="text",
    outputs="text",
).launch(
    favicon_path="lion.jpg",
)

[omerXfaruq]

good job👍

[omerXfaruq]

I am not sure about this but weren't we doing some checks to file paths to not access to different paths within user's computer?
like os.some_function

[abidlabs]

Yes, I thought about this as well. In this case, we don't have to worry about that because the favicon route only returns a fixed filepath that is specified by the demo creator. Where this can become a security concern is if a demo user can request a file at an arbitrary path (like in the /file/ route)

[abidlabs]

Going to add a default favicon, as suggested by @pngwn, thanks!