Preserve order that plugins are applied in Gremlin Console

Plugins are now loaded in the order that ServiceLoader constructs them. Would be better if the plugins respected the order of the configuration file, that way the user could expect some control there in case one plugin depended on another for some reason. It's not a perfect system as users would be responsible for ordering, but it's a cheap, non-breaking way to at least provide some method for dealing with dependencies.