Fix rubocop offenses in app/helpers

[JadeDickinson]

Fixes #6436

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[JadeDickinson]

There were a few Metrics/ offenses I left outstanding, as these seemed impossible to address without significantly changing the code:
Metrics/AbcSize
Metrics/MethodLength
Metrics/ModuleLength

[pydevsg]

@jywarren do give a review, though a few cases aren't running. Good work @JadeDickinson

[SidharthBansal]

There are some conflicts. Kindly fix them

[SidharthBansal]

Can you please make different prs instead of one pr?
That will be easy to review and merge
Thanks

[SidharthBansal]

As the person is inactive for more than a month, I am closing the PR. In case you want to push changes please feel free to open a new PR OR reopen this PR and add additional changes to it.
Thanks for contributing on Public Lab