Please add IPFS Cluster as a pinning service alongside Piñata

Since ipfs-cluster-service is readily available for users to install on their own servers, it should be easier to set up in the web UI: not a custom service, but a primary supported one.

There are some vague docs here: http://ipfscluster.io/documentation/reference/pinsvc_api/ The process to get a "secret access token" is to use basic auth first. So maybe it's better to have UI for doing that too? If one is setting it up for the first time on a local network, providing user and password would be a good place to start; after that's been done once, and the UI has downloaded the auth token, it should offer to save it to a file for next time, and for use outside the local network.