fix: Issues with inconsistency in case conversion

[joshthoward]

Summary of Changes

Fixes issues with inconsistency in case conversion, specifically issues #758 & #596

Tests

No new test were added, expected output in some tests were updated to reflect the removal of the case conversion. Deprecation warnings for self.assertEquals() were resolved by replacing with self.assertEqual().

Documentation

N/A

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[feng-tao]

thanks @joshthoward !

[joshthoward]

NP

There are two things that should be noted for future reference:

1. I left the tag case conversion in the model code here. It seemed to make sense for displaying tags.
2. Case conversion going forward should be done by extractors if needed. There is a precedent for this here.

@feng-tao Just as a point of curiosity, how do you see the versioning updating upon release given that this is a potential breaking change to the data model?

[feng-tao]

we could do 4.0.0 in next release. cc @allisonsuarez @dikshathakur3119