Remove one debug message

Mojo's default log level is debug, and our startup logs a few debug
messages, which are then displayed every time we run "./app cmd". It's
not worth fixing the larger problem right now (how would we do it?), but
removing one somewhat useless debug message is a reasonable first step.
Add a generic command to create a user

The role-name handling is a bit clumsy (it tries to load App::User to
find recognised role names, falling back to Gadwall::User), but it's
good enough for the moment.
Might as well add a users.name column now
Make the full name optional