FEATURE: Add button to delete unused tags

[davidtaylorhq]

This is particularly useful if you have uploaded a CSV file, and wish to bulk-delete all of the tags that you uploaded.

Adds an option to the tag administration hamburger:

Clicking the button presents a confirmation modal, including the number of tags which will be deleted:

[discoursebot]

You've signed the CLA, davidtaylorhq. Thank you! This pull request is ready for review.

[gschlager]

This needs pluralization with one and other keys.

[tgxworld]

I'm wondering if it would be better to list the names of the unused tags instead of just displaying the count.

[davidtaylorhq]

Thanks for the feedback. I have made the changes.

• Tags are listed in the confirmation:

• If there are more than 20, it says "and # more"

• Strings have 'one' and 'many' entires. @gschlager can you check that looks ok? There are two numbers in the delete_unused_confirmation_more string, but {{total}} will always be greater than 1

[ZogStriP]

• If there are more than 20, it says "and # more"

😍

[gschlager]

Unfortunately 2 numbers won't work for languages like Russian where you have other categories than one and other. For example, if total is 31 it would require the one category for {{total}} and the many category for %{count}.

Possible solutions:

1. Use Message Format which is totally awesome, but super hard to translate.
2. Split up the translation. I think you could get away with that option in this case by using the following strings:

      delete_unused_confirmation:
        one: "%{count} tag will be deleted: %{tags}"
        other: "%{count} tags will be deleted: %{tags}"
      delete_unused_confirmation_more_tags:
        one: "%{tags} and one more"
        other: "%{tags} and %{count} more"

And use it like this:

  const string = I18n.t("tagging.delete_unused_confirmation", {
    count: tags.length,
    tags:
      more === 0
        ? tagString
        : I18n.t("tagging.delete_unused_confirmation_more_tags", {
            count: tags.length,
            tags: tagString
          })
  });

💡 Two more tips:

1. {{key}} is deprecated. Use %{key} whenever possible.
2. Instead of using the number 1 inside the one category, it's good practice to always use %{count}. It makes it easier for translators who always need to use %{count} for their language. See Always use %{count} variable when translating pluralized strings.

[davidtaylorhq]

Amazing, thanks for the info @gschlager - I've made those changes in ba00fcc (sorry I got a bit trigger-happy with the merge button!)