Fix server error reporting in find_friends
Add PersonaNotFoundError to Nucleus/Vesicle

* Is raised when a needed Persona object is not found
Reorganise configuration

* Only static/no interdependent config options are set in *_config.py
* web_ui/__init__.py handles more complex settings, including cmd line
arg parsing
* app.soma => app.souma
Autoload Persona info if missing for Vesicle verification/signing