Read the ClassPath from Plist property

This is based on a contribution by Philipp Holzschneider. Thank you very much, Philipp!

ClassPath reading and setting works for the following two plist styles:

Either a single `<string>`:
```xml
<key>Java</key>
<dict>
  <key>ClassPath</key>
  <string>$JAVAROOT/jarFile.jar</string>
</dict>
```
or an `<array>` of Strings:
```xml
<key>Java</key>
<dict>
  <key>ClassPath</key>
  <array>
    <string>$JAVAROOT/jarFile.jar </string>
    <string>$JAVAROOT/</string>
  </array>
</dict>
```

Oracle Plist with Oracle AppBundler doesn't support setting the ClassPath. It will only copy all ClassPath-Resources into the App-Bundle itself and then set the ClassPath to this Java-Folder.