Optional toggles are unselected if a user sorts table on flag tab

[cristinamullin]

Is your feature request related to a problem? Please describe.

When usability issue #160 was addressed, the sorting feature was added to the flag table.

Now, if a user selects any Flag Reason to Switch 'On' to flag for removal, and if a user then proceeds to try to sort by any column -- for example, if a user wants to toggle on "Coordinates are imprecise (less than three decimal digits) (see TADA.SuspectCoordinates.Flag)" and then they sort by 'Results affected', that toggle then gets deselected.

Describe the solution you'd like

I think it would be good if it's the case when a user selects to toggle a flag, if they were to then sort, the toggles that they've chose would stay the same.

Reminders for TADA contributors addressing this issue

New features and/or edits should include the following work:

• Create or edit the code.

• Document all code using line/inline and/or multi-line/block comments
  to describe what is does.

• Create or edit tests in tests/testthat folder to help prevent and/or
  troubleshoot potential future issues.

• If your code edits impact other functionality in the shiny
  app, ensure those are updated as well.

• Run styler::style_pkg(), devtools::document(), and devtools::check()
  and address any new notes or issues before creating a pull request.

[cristinamullin]

This looks helpful: https://stackoverflow.com/questions/27965791/how-to-save-sorting-in-datatable-in-shiny