[WIP] FEATURE: Add site setting to show more detailed #404 errors. (PR #8014)

If the setting is turned on, then the user will receive information about the subject: if it was deleted or requieres some special access to a group (only if the group is public). Otherwise, the user will receive a generic #404 error message. For now, this change affects only the topics and categories controller.

This commit also tries to refactor some of the code related to error handling. To make error pages more consistent (design-wise), the actual error page will be rendered server-side.


Preview

  • Topic in a secret category (with public group)

topic in secret category

  • Deleted topic in a public category (with public group)

a deleted topic

  • Deleted topic in a secret category

deleted topic in secret category

  • Topic in a secret category (with private group)

topic in super secret category

  • Secret category (with a public group)

category page

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