Change: Intro Python (Rainforest) and Intro Python (Savanna) have been shortened

Based on feedback from CodeHS teachers and students, the Introduction to Computer Science in Python courses (Rainforest and Savanna) have been shortened to be more appropriate for a first time, year long introduction to computer science in Python. The courses now end with the Hangman project, and a few of the more challenging exercises have been removed.

The extra units of the course (Classes and Objects, and the Who Said It? Project) are still available as Supplemental Materials in both of these courses. This means that advanced students can still move on and take the more advanced material if they finished the course early.