REVIEW: [NX-408] Add nexus karaf branding

https://issues.sonatype.org/browse/NX-408

```
Sonatype Nexus (3.0.0-SNAPSHOT)

Hit '<tab>' for a list of available commands
and '[cmd] --help' for help on a specific command.
Hit '<ctrl-d>' or 'system:shutdown' to shutdown.
```
k, will remove, was just following examples on http://karaf.apache.org/manual/latest/developers-guide/branding.html