Create a docker container / coopcloud recipe

[fauno]

Some time ago we talked about a collabortion with them would be creating a Coopcloud recipe for the Social Inbox, but we didn't add it to an issue, so here it is.

I've been working with it lately so it's at hand, though I understand it's low priority :)

Steps:

• Create and publish a Docker container for the Social Inbox
• Create a docker-compose.yml using this container (both can live on this repo)
• Add a recipe to coopcloud