Add Docker environment & web demo

[bfirsh]

Hey @ericsujw! 👋

This pull request makes it possible to run your model inside a Docker environment, which makes it easier for other people to run it. We're using an open source tool called Cog to make this process easier.

This also means we can make a web page where other people can try out your model! View it here: https://replicate.ai/ericsujw/instcolorization

You can claim your page by signing in with GitHub, then we'll feature it on our site.

I've also added a little script to download the COCO segmentation weights, so they don't have to be downloaded a predict time.

In case you're wondering who I am, I'm from Replicate, where we're trying to make machine learning reproducible. We got frustrated that we couldn't run all the really interesting ML work being done. So, we're going round implementing models we like. 😊

[zeke]

Wow this is a really cool model!

@ericsujw what do you think of this PR? Have you had a chance to look at it yet?