Fix/pmftxyz eq ors normalization

[vyasr]

Description

Store and use the last number of equivalent orientations to normalize the PMFT. This PR should be merged after #615 and only following discussion regarding whether this solution is appropriate on #616.

Motivation and Context

Resolves: #616.

How Has This Been Tested?

Updated existing test to include checking the behavior when multiple equivalent quaternions are specified.

Screenshots

Types of changes

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

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have updated the documentation (if relevant).
• I have added tests that cover my changes (if relevant).
• All new and existing tests passed.
• I have updated the credits.
• I have updated the Changelog.

[codecov]

Codecov Report

Merging #619 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #619      +/-   ##
==========================================
+ Coverage   92.78%   92.87%   +0.09%     
==========================================
  Files          16       16              
  Lines        2189     2189              
  Branches       32       32              
==========================================
+ Hits         2031     2033       +2     
+ Misses        146      144       -2     
  Partials       12       12              

Impacted Files	Coverage Δ
freud/pmft.pyx	98.92% <0.00%> (+1.07%)	⬆️

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[bdice]

I'd like to have some discussion on #619 before we accept this solution.

[vyasr]

I'd like to have some discussion on #619 before we accept this solution.

I assume you mean #616 as mentioned in the PR.

[bdice]

LGTM, unless there's further discussion on #616.