Fixed bug that prevented next_record and prev_record from using custo…

[rossmechanic]

…m manager names

Description

The manager name history had been hardcoded in the function calls for get_next_record and get_prev_record. This PR uses utils.get_history_manager_for_model to allow these functions to be used with custom manager names.

Related Issue

Fixes #500

Motivation and Context

Bug fix.

How Has This Been Tested?

Added tests for next_record and prev_record on a model with custom manager name

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the make format command to format my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #501 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #501      +/-   ##
==========================================
+ Coverage   97.22%   97.23%   +0.01%     
==========================================
  Files          16       16              
  Lines         721      724       +3     
  Branches       95       95              
==========================================
+ Hits          701      704       +3     
  Misses         10       10              
  Partials       10       10

Impacted Files	Coverage Δ
simple_history/models.py	99.22% <100%> (ø)	⬆️

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[barm]

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