Install a pre-push hook for removing unpm

[mcnuttandrew]

It is really easy to accidentally break the react-vis build by forgetting to remove unpm delivered packages. This has happened many many times. This PR adds pre push hook stop unpm packages from entering a PR.

This can also be used to create other hooks (like a prepublish hook that we've sought for a long time).

I don't know too much about husky, but it looks legit and the folks who use it are credible. Let me know if you have any thoughts.

[benshope]

Looks great! I was looking at the commit hooks situation and was going to use husky also, so I already know that's a good choice. Make sure the package addition is reflected in the npm lockfile also.