Add "share audio" option for audio-only chapters

In our trc app we are using audio-only for some books since we are in the process of revision so the existing Paratext text and the audio donꞌt match, but we want to make use of the existing audio until the revision and re-recording is completed. It would be nice to have a “share audio” button to be able to easily share with others the mp3 file for an entire chapter.