Feature request: negative prompts in web browser demo

[Hinaichigo]

It would be nice if you could also do negative prompts in the demo web ui.

[RubenGarcia]

Can you do negative prompts in demo.py?

[RubenGarcia]

https://github.com/Drake53/stable_diffusion.openvino has negative weights. Can this be merged here?

[csiefer2]

@Hinaichigo @RubenGarcia Added a PR to merge that bit from Drake53.