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.
I think it would be possible to improve the name here. Perhaps `Stager` even?

Note: I really dislike using the terms "helper", "util", "default" etc. - they become dumping grounds.