Custom JSON Marshal/Unmarshal for Account Types

[alexanderbez]

closes: #5270

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• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Re-reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #5280 into master will increase coverage by 0.84%.
The diff coverage is 83.12%.

@@            Coverage Diff             @@
##           master    #5280      +/-   ##
==========================================
+ Coverage    53.5%   54.35%   +0.84%     
==========================================
  Files         290      290              
  Lines       17771    17899     +128     
==========================================
+ Hits         9509     9729     +220     
+ Misses       7511     7396     -115     
- Partials      751      774      +23