Conversations doesn't set Priority, in that case assume it's zero:
If no priority is provided, the processing server or client MUST
consider the priority to be zero ("0").
https://tools.ietf.org/html/rfc6121#section-4.7.2.3
TODO:
- Registration does not support enabling/disabling different features
- Avatar does not work at all
- Check all he configurable options are really used