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: Documentation update for https://github.com/archivesunleashed/aut/pul… aut-docs#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]

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%           
=======================================
  Files          44       44           
  Lines        1297     1297           
  Branches      250      250           
=======================================
  Hits         1088     1088           
  Misses         80       80           
  Partials      129      129           

[ianmilligan1]

Looks good to me; I'll defer to @ruebot and @lintool whether they should be capitalized file extensions or not in WriteGexf and WriteGraphml (a quick read of PEP8 doesn't seem to give a definitive answer but you would both be more familiar with this).