[iOS] expose api to request for micorophone, and a callback for when we have it.

[mikehenrty]

We could even attach the permission prompt to the first time I call "start_capture".

[mikehenrty]

@andrenatal or @mbebenita, would either of you be able to have a look?

[mikehenrty]

The reason I think this is important is because I think Apply looks at UX in their decision making process, and prompting for a mic without user action is bad UX.

[andrenatal]

@mikehenrty This was fixed here. So now the permission request is handled when you call start_capture.

I also introduced a new callback to send messages to the webapp so those can be displayed properly to the user.

[andrenatal]

@mikehenrty Currently are being sent the following messages:

• errorplaying: if the audio file could not be played
• capturestarted: when the mic starts recording
• errorrecording: when some error happened when started recording
• nomicpermission: when the user denied permission to record