Hook for buffering on mobile

[liamcrean]

Hello

I wondered if there was a way to hook into the UI so I feedback to user that a track is buffering (could add loading spinner) — would be great on mobile where native IOS waits for the track to fully buffer before playing - so the intial wait needs an indicator on top of buffer

Thanks. Liam

[liamcrean]

This realates to the bug I reported — #401