Rework pkg/log, add 'loglevel' and 'logdate' flags, streamline

- removes some previously added manual location strings: now handled by pkg/log depending on loglevel
- kept manual string locations on fmt print functions
- add 'notice' and 'critical' loglevels
- add 'Panic' and 'Panicf' functions to log panics
- adresses issue #26

internal/auth/users.go

@@ -67,7 +67,7 @@ func (auth *Authentication) AddUser(user *User) error {
 		return err
 	}
 
-	log.Infof("AUTH/USERS > new user %#v created (roles: %s, auth-source: %d)", user.Username, rolesJson, user.AuthSource)
+	log.Infof("new user %#v created (roles: %s, auth-source: %d)", user.Username, rolesJson, user.AuthSource)
 	return nil
 }