Update Smack to 4.0.6

I'm aware that the changes to the method signatures regarding exceptions means an API breakage. I leave it up to the mule devs to decide how to proceed. Basically I see three options:

- Use the "new" API in the next major Mule version (that's my prefered solution)
- Use the "new" API in the current Mule version
- Wrap the exceptions so that the API stays the same