Use docker volumes and not binding for services

[antho1404]

The actual system is using binding for services volumes. In our case we don't really need to bind the folder to a specific path on the host machine and this add a lot of complexity on the configuration of this docker container.

The docker socket sent to the core container is still using the bind mode but other volumes are now using the new default value from docker volume and not bind anymore. This means that all the volumes that need to be mounted on a service will no longer be present in ~/.mesg/services but will be managed by docker.

This will be helpful for the PR #416

fix #125

[NicolasMahe]

It's working well, so I approve.

But, we don't provide any way to delete the volume. I suggest to delete the volume with the API deleteService. I will create an issue.