REVIEW: [NX-408] Add nexus karaf branding

https://issues.sonatype.org/browse/NX-408

```
Sonatype Nexus (3.0.0-SNAPSHOT)

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```
The `Import-Package` default is already `*`, so you can drop that line. Similarly setting `Private-Package` to `!*` shouldn't be necessary here, the default setting should be fine.