Replaced nodelist and nodemap in CLI with mn

Also, updated Mininet to be more compliant with dict
Fixes #182

We need to talk about the semantics for Mininet because they aren't quite the same as dict. This isn't necessarily a bad thing, but it could be confusing. Usually for a dict, the iterator is over the key set. Mininet's iterator is over the values. We use the iterator of the values much more frequently, so it saves keystrokes and extra lookups.