We can now show replay buttons for the audio contained in {{FrontSide}}
without having to play it again when the answer is shown.
The template code now always defers FrontSide rendering, as it wasn't
a big saving, and meant the logic had to be implemented twice.
This simply wraps the field in extra text that the frontend will
deal with. Also added some helpers for extracting and stripping
audio and TTS tags from the rendered text.
