[SD-1119] Adding default role to new user.

Thanks for highlighting this Ioan. You are right that we probably don't need to it every find_one event:

These are the few places user.find_one is used from 
* /api/user/_id endpoint where UI gets the user
* auth.py from check_permissions function 
* preferences.py to get the user settings, now returns the active_privileges
* Change password service

The first one may not be needed as depending on the UI we can have either a new endpoint to get the privileges or we can use the preferences.

It is needed everytime auth.py gets the user
It is needed everytime preferences.py is called.
It is not needed when change password is called.

So I'll make the change to remove the computing from find_one to make it explicit.