gui.py: Create New User throws Tkinter exception

[bpkempke]

When trying to create a new user on a fresh install, the following is thrown:

Exception in Tkinter callback
Traceback (most recent call last):
File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1535, in call
return self.func(_args)
File "/home/bpkempke/repos/M-ulator/platforms/m3/programming/m3_logging.py", line 80, in inner
return fn(_args, **kwargs)
File "./gui.py", line 403, in create_new_user
if uniq in self.users:
AttributeError: 'Configuration' object has no attribute 'users'