Remove dependency of data container from ethereum container

[slundqui]

Currently, the data container (i.e., chain -> postgres container) specifies a dependency on the ethereum container. Unfortunately, this means that the data container cannot be restarted (by bringing down and back up) without brining down the ethereum container. While the data container is able to be started/stopped based on the state of postgres, ethereum loses all state when brought down.

Here, the solution is either remove the dependency, or to allow the ethereum container checkpoint and reboot from state.