Allow changing Constellation Config through environment variables

[Hobadee]

Allowing the changing of the Constellation Config through environment variables would likely help out in automated clusters.

Perhaps a comma-separated list as an environment variable?

Example of the config file JSON:

{
  "ConstellationRole": {
    "RoleEnabled": true,
    "DeleteUnusedData": false,
    "Servers": [
      {
        "Type": "comet",
        "Description": "localhost",
        "RemoteAddress": "$self$"
      }
    ]
  }
}

Depends on #2