Make breadcrumbs show specific parents when they exist

[willbarton]

This PR changes the way TreeModelAdmin generates breadcrumbs. Where before the crumbs would include only the plural name of the parent models, even if we're "inside" a particular parent. This PR changes the breadcrumbs to display str(parent_instance) instead of the plural name of the model.

The test app before:

The test app after:

I've bumped the version number in setup.py in anticipation of releasing this.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the development playbook
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

[coveralls]

Pull Request Test Coverage Report for Build 53

• 6 of 6 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 100.0%

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Totals
Change from base Build 32:	0.5%
Covered Lines:	208
Relevant Lines:	208

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💛 - Coveralls

[willbarton]

With Reguations 3000:

[higs4281]

It's helpful to be able to see where you are.