Support Saving of Mindmaps

```
All Mindmaps should be saveable.
Finish implementation of
de.uniwuerzburg.informatik.mindmapper.spi.XmlFileSaver.saveDocument in
MindMapperSpi

```

Original issue reported on code.google.com by `bl...@informatik.uni-wuerzburg.de` on 4 Nov 2008 at 12:14
