Simplify lab 4 and 5

[alexhanna]

Lab 4 and 5 seemed to cause learners some undue stress because they were being asked to reperform some operations from past labs and it wasn't adding much to the current lesson.

Lab 4

• Limited task 1 -- asking them to only produce a list of CSV headers. The rest of the to_csv has been provided.
• Altered task 2 such that it has to do with filling in details of the Apache Beam pipeline, rather than addressing the SQL again.

Lab 5

• Provided the majority of the code for task.py inline in the notebook and instead asked them to add three command-line arguments.
• Provided the majority of the code for model.py inline in the notebook and instead asked them to fill in parts where the hardcoded numbers are replaced with hyperparameters.

[lakshmanok]

Thanks, Alex. Looks great!

(1) Could you make sure to add a "TODO" to everything that you want them to do?
For example, the beam BigQuery line simply says "Change this".

(2) Instead of:
%writefile -a babyweight/trainer/model.py
could you use:
%writefile babyweight/trainer/model.py
(i.e. without the -a) and the entire content of model.py and task.py in the notebook?
The reason is that, otherwise, if they make a mistake and rerun the cell, things will keep on being appended and not replaced.

(3) Once you put the entire content of model.py and task.py in the notebook, you can do a "git rm" to yank those files off the repository

[alexhanna]

@lakshmanok -- good call on writefile vs writefile -a. The last commit should address all of those.