Reimplement Classes as simplified (not-fully-functional) ordered set

Classes is essentially an ordered set, but we only need very limited
functionality, so keep it simple and provide only the very basics.

Purposely, Classes no longer derives from list so as to not give a false
impression.

Also, switch from nose to unittest.

Signed-off-by: martin f. krafft <madduck@madduck.net>
5 files changed