Wip/autoplugins

This is a work-in-progress pull-request. Feel free to add suggestions, corrections and ideas for the autoplugins. The current structure is

```
SbtNativePackager
    UniversalPlugin
        WindowsPlugin
        DockerPlugin
        LinuxPlugin
            RpmPlugin
            DebianPlugin
                DebianNativePackaging
                JDebPackaging
    AkkaAppPackaging
    JavaAppPackaging
        JavaServerAppPackaging
```

I will update the `Keys` here, when I have a final structure and everything works the first time.
Here's a fun bootstrapping issue.  Play will be duplicating your settings, so it's six-half-dozen-the-other right now whether the "play old version of our settings" or "current version of settings" gets used here....