Fix for duplicate logs.

[audiodude]

Fixes #83

This bug was introduced when we switched from doing unseen articles after each quality/importance run, to doing them all at the end. Because of that, the old_rating doesn't get updated in between runs. So, when a new article appears that has both a quality and an importance rating, the rating for quality would be written, then it would be re-written with importance as a "new" rating, which would set the quality to NULL.

This manifests as duplicate logs because the next day, the old_rating is there, but has quality NotA-Class, so we write a log that the quality went from NotA-Class -> Whatever, which shows up in the logs as "assessed".

[codecov]

Codecov Report

Merging #84 into master will increase coverage by 0.01%.
The diff coverage is 97.22%.

@@            Coverage Diff             @@
##           master      #84      +/-   ##
==========================================
+ Coverage   95.47%   95.49%   +0.01%     
==========================================
  Files          31       31              
  Lines        1924     1952      +28     
==========================================
+ Hits         1837     1864      +27     
- Misses         87       88       +1

Impacted Files	Coverage Δ
wp1/logic/project.py	87.26% <100%> (ø)	⬆️
wp1/logic/project_test.py	98.65% <100%> (+0.06%)	⬆️
wp1/logic/rating.py	97.1% <90%> (-1.34%)	⬇️

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