Revert "[#48721683] QuestionsController requires a non-finalised survey to do anything other than `show` and `index`."

This reverts commit 9a950db05fd96bc5d1d745b4132ca37c742d93b4.
[#48721683] A question can't be destroyed, updated or created if its survey is finalised.

- Implemented using callbacks instead of controller filters.
[#48721683] Fix specs so they create questions for a survey only when it
is NOT finalized.