Code refactoring

[jshjohnson]

Description

• Reduce complexity of _addPredefinedChoices
• Add JSDoc comments to utils
• Remove legacy placeholder attributes from demo page

Screenshots (if appropriate)

Types of changes

• Chore (tooling change or documentation change)
• Refactor (non-breaking change which maintains existing functionality)
• 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 not work as expected)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #735 into master will increase coverage by 0.07%.
The diff coverage is 45.45%.

@@            Coverage Diff             @@
##           master     #735      +/-   ##
==========================================
+ Coverage   66.46%   66.53%   +0.07%     
==========================================
  Files          22       22              
  Lines        1309     1306       -3     
==========================================
- Hits          870      869       -1     
+ Misses        439      437       -2

Impacted Files	Coverage Δ
src/scripts/actions/groups.js	100% <ø> (ø)	⬆️
src/scripts/components/list.js	24.32% <ø> (ø)	⬆️
src/scripts/actions/items.js	100% <ø> (ø)	⬆️
src/scripts/actions/choices.js	100% <ø> (ø)	⬆️
src/scripts/store/store.js	92% <ø> (ø)	⬆️
src/scripts/actions/misc.js	100% <ø> (ø)	⬆️
src/scripts/components/container.js	100% <100%> (ø)	⬆️
src/scripts/components/input.js	100% <100%> (ø)	⬆️
src/scripts/lib/utils.js	75.75% <14.28%> (+1.51%)	⬆️
src/scripts/choices.js	54.22% <50%> (-0.16%)	⬇️
... and 1 more

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