The actual creation of the `MultiChunker` should not happen in the Config class. Instead, it should be in a factory?

Maybe like: 
- https://github.com/binwiederhier/syncany/blob/19de9a85ba551e26028a4b08067e2cc49873dcb1/syncany-lib/src/main/java/org/syncany/connection/plugins/Plugins.java#L126
- or better yet: https://github.com/binwiederhier/syncany/blob/19de9a85ba551e26028a4b08067e2cc49873dcb1/syncany-lib/src/main/java/org/syncany/chunk/Transformer.java#L112

In particular, it should be very similar to how Chunker and Transformers can be instantiated.