ExtensibleTypes

I added an extensible type to a component. Code wise it looks good. I see the extensible type. XML wise looks a little wierd.
```

.....

```

I would have expected it to be

```

.....

```

And when attempting to read back in the bom.xml file, sure enough the extensible type is no where to be found.

Start by reproducing the XML serialization and readback described in the issue, comparing the current packageManager output with the expected extensibleTypes structure. Trace how the BOM is written and parsed, then verify that the extensible type is emitted in the expected nesting and recovered when bom.xml is read.

Vom Indexierungsmodell aus dem Issue-Text verfasst.