Support for assembly-style FileSets.

Includes ability to include additional files (like configuration or scripts) in the capsule jar by specifying them in fileSets:

```
<fileSets>
    <fileSet>
        <directory>config/</directory>
        <outputDirectory>config/</outputDirectory>
        <includes>
          <include>myconfig.yml</include>
        </includes>
    </fileSet>
</fileSets>
```