Edit published questions: create new question versions

FEATURE: Allow editor to edit a previously published question, thus creating a new version for it

• create new graphql endpoint for creating new question version
• add resolver and controller methods to respond to the endpoint
• modify createNewVersion method in the modal to check if previous version for that question exist:
  • if yes, copy its data into the new version and return it
  • if no just create a new version with no data (as when creating a new question)
• create mutation in the client to create new question version
• use the mutation in Question page
• modify Question ui component with the following:
  • add Edit Question button if question is published and user is an editor
  • confirmation modal with warning that they're about to create a new question version
  • if editor confirms, call onCreateNewVersion method, received by props

closes #95 (closed)