Watch for contract changes to run deploy/test

[ByteAtATime]

I believe a nice QoL feature would be to have a command to automatically deploy/test contracts when they change. I'm definitely down to submit a PR for this, but I'm thinking we use nodemon for watching/command running. I would definitely consider this a "minor change", but just wanted to open a discussion for whether this is needed and if my approach is valid.

I was thinking we add two extra commands, each one listening to changes in the contracts and deploy directories:

1. yarn deploy:watch, which runs yarn deploy every time the contracts/deploy scripts change
2. yarn hardhat:test:watch or yarn hardhat:test-watch, which runs yarn hardhat:test every time any of the contracts, deploy scripts, or tests change

Regarding the second command, I'm not sure if I'm a fan of the triple colons, but I'm not sure what the best way to deal with this would be. Again, whatever method we end up with, I'll create a PR!

[carletex]

yarn deploy --watch is already doing (1).

I think (2) is not worth it, especially if we need to add an extra dep.