use js-ipfs remote pinning api

[yusefnapora]

Right now, minty is using an HTTP client I wrote for the remote pinning service API. I've got a PR open for js-ipfs to add support for remote pinning, which is how we'd prefer people actually do things.

Ideally, we'll have at least an experimental release of js-ipfs with the remote pinning API available to depend on sometime next week, so we can use it in the tutorial.