REVIEW: Add support to automatically exclude dependencies from plugin bundles

With this change, and this configuration on the plugin:

    <bannedRootArtifactId>org.sonatype.nexus:nexus-plugin-api:jar:${nexus.version}</bannedRootArtifactId>

... nexus-plugin bundle .zips will automatically exclude dependencies which are provided by NX core, ie:

```
[INFO] --- nexus-plugin-bundle-maven-plugin:1.0.1-SNAPSHOT:generate-metadata (default-generate-metadata) @ nexus-siesta-plugin ---
[INFO] Including 1 plugin dependencies:
[INFO]  + org.sonatype.nexus.plugins:nexus-ui-extjs3-plugin:jar:2.6.0-SNAPSHOT
[INFO] Banned 3 dependencies:
[INFO]  - org.codehaus.jackson:jackson-core-asl:jar:1.9.12
[INFO]  - org.codehaus.jackson:jackson-mapper-asl:jar:1.9.12
[INFO]  - org.sonatype.sisu:sisu-inject-bean:jar:2.3.4
```