Various tutorial improvements

[jwmueller]

Another round of many tutorial improvements such as:

• Not having weird reshape in forward pass of MNIST ConvNet (also verified this works with the LearningWithNoisyLabels).
• Removing seemingly unnecessary TF logging suppression line in audio tutorial
• Moving the hidden tests to the end of tutorials and add tests to ensure LNL improves the model accuracy.
• Language and code improvements throughout tutorials.

Apologies for making PR from branch, my fork's master branch is occupied by open PR in limbo (was made from plane with bad internet)

[codecov]

Codecov Report

Merging #173 (09bbf75) into master (7247b09) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   87.65%   87.65%           
=======================================
  Files          12       12           
  Lines        1021     1021           
  Branches      192      192           
=======================================
  Hits          895      895           
  Misses        104      104           
  Partials       22       22           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7247b09...09bbf75. Read the comment docs.

[weijinglok]

Overall looking good! just one comment to be addressed!

[weijinglok]

LGTM!