fix: multiple small improvements to the wizard
- Move the wavs question after fully processing the filelist, including
permission.
- Catch the case where we don't have permission to write the directory with a
friendly error message.
- Make the ValidateWavsStep question use the same type of prompt as the other
similar questions, for better UX consistency
- If we accept a wavs dir / filelist combo with missing wav files, give a
bright error message to make it clear future problems will happen.
- Don't save the config if no dataset was created.
- Delete the output directory in the OutputPathStep so we don't leave an empty
directory lying around when we abort without saving, for any reason. (SL
request, for something that's been bugging me for quite a while!)
- Clarify various message texts based on SL PR review feedback.
