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.
SO I might do two things:

1. I'd have this be autoenabled, so debian *has* a packager by default
2. Mark JDeb packaging as conflicting with this one (requires = !DebainNativePackaging)

This should mean when users enable JDeb, it disables DebianNative from being included.