PEP8 Python app method names.

[ruebot]

GitHub issue(s): #468

What does this Pull Request do?

Renames app names.

How should this be tested?

• Documentation update PR: https://github.com/archivesunleashed/aut-docs/pull/67
• https://github.com/archivesunleashed/notebooks/blob/master/PySpark%20-%20Extract%20Popular%20Images.ipynb
• https://github.com/archivesunleashed/notebooks/blob/master/PySpark%20-%20aut%20standard%20derivatives.ipynb

[codecov[bot]]

Codecov Report

Merging #477 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #477   +/-   ##
=======================================
  Coverage   83.88%   83.88%           
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  Files          44       44           
  Lines        1297     1297           
  Branches      250      250           
=======================================
  Hits         1088     1088           
  Misses         80       80           
  Partials      129      129