remove balanced trees

This has been moved to the lecture portion of the course.
Summarized balanced tree in two sentences.
revisions to linked lists

1. Always inherit from object in code we give to students!
2. Circularly-linked is not important enough to talk about.
3. Avoid reusing variable names (like counter).  self.counter vs counter
can be confusing.
4. Use the proper class functions when possible (__len__ for example).
5. Removed complexity jargon.  Replaced with scale of very efficient,
efficient, and very inefficent.