Remove material on looping over indexes

This material can be covered in response to questions.
Use single backtick quotes throughout Intermediate Python lectures
Minor editorial cleanup to the first Intermediate Python lecture
Say that .iloc means integer location when introducing Pandas
Split demonstration of DataFrame methods into separate code blocks

This demonstrates the methods one at time making it easier to
follow and also makes the output clearer.
Intermediate Python lectures are for those who have programmed before.

Mention this up front.
Describe difference between Python printing and Notebook displaying.
Execute code block after error message in first Int. Python lecture
Improve display of final figure in first Int Python lecture