Install arbitrary docker app via a link to yaml file

[mehrdadfeller]

So far the end user can install dockers apps from a list of offered containers out of the box. Alternatively they can install portainer and use that to install other docker containers.

I believe we need to add a third way to seamlessly fetch and install a docker container by scanning a QR code that links to a yaml config file. These can be served on a Github gist or any endpoint. The user should include all necessary config params and credentials in their yaml file.

Let's discuss the details here and work out the specs.