Allow gradio users to submit multiple requests

[rahimnathwani]

Adding demo.queue(concurrency_count=1) tells gradio to queue up requests when one is already running. This means you can queue multiple requests before going to bed, without worrying that your GPU will run out of memory.

[ajr-dev]

I favor this, but more for the reason of having multiple people queued. I for one like to share my gradio link with friends, if they can be queued, that'll be neat.