Delete old thumbnails from the media/cache directory and the database

[LarryMartell]

Address issue #721

[uri-rodberg]

Do you know why tests failed or canceled?

[uri-rodberg]

@LarryMartell Can you rebase your PR on branch master?

[LarryMartell]

@LarryMartell Can you rebase your PR on branch master?

Done

[codecov]

Codecov Report

Merging #733 (d11b110) into master (4e77896) will decrease coverage by 0.67%.
The diff coverage is 38.70%.

❗ Current head d11b110 differs from pull request most recent head 337a51f. Consider uploading reports for the commit 337a51f to get more accurate results

@@            Coverage Diff             @@
##           master     #733      +/-   ##
==========================================
- Coverage   74.11%   73.45%   -0.67%     
==========================================
  Files          30       30              
  Lines        1700     1729      +29     
==========================================
+ Hits         1260     1270      +10     
- Misses        440      459      +19     

Impacted Files	Coverage Δ
sorl/thumbnail/management/commands/thumbnail.py	81.13% <33.33%> (-18.87%)	⬇️
sorl/thumbnail/kvstores/base.py	87.27% <40.00%> (-7.52%)	⬇️
sorl/thumbnail/conf/defaults.py	100.00% <100.00%> (ø)

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[uri-rodberg]

Please wait with this PR and don't do anything until we finish merging #739 .

[uri-rodberg]

@LarryMartell Please contact me by email. Your mailbox is full.

[uri-rodberg]

I'm closing this PR. There is a new PR - #740.