Homework: Add support for multiline setup/answers

[dolsysmith]

In autograder.py, script should support multiple setup cells for a given problem, to increase readability.

[dolsysmith]

In addition, deleting the tagged cell in the process of entering one's answer causes the autograder to fail, even if the tests pass in the notebook.

Solution:

1. Autograder runs the tagged/commented cells first. If tests pass, exit.
2. If tests fail, re-run by running all cells. If tests pass, exit.