Adding native audio recording for `audio` type questions

[Tino_Kreutzer]

@chrissyhroberts

• The audio recorder saves a copy of the recording to disk, which has to be manually removed. At present our teams collect a lot of sensitive health data interviews and use RecForge Pro II. It is a very messy process to clean up the files after saving.

This should be taken care of by Remove previously taken images from gallery which should be implemented soon. (It will be not just images but all attachments.)

• Audio files get big very quickly, putting strain on ability to upload media files with limited bandwidth. The Opus format sounds promising if 1 hour of interview comes in at less than 5 MB, but I haven't worked with Opus before and I would love to test an APK to see how this works in the field.

RecForge II allows recording in opus, but strangely only in 48kHz. I've had very good results recording voice with AMR/3gp, though Opus claims to be even smaller. In my work AMR required 0.1 MB per minute at phone quality, which would be small enough for field contexts. Higher quality would be good for multi speaker or bad recording environments, though. This is why allowing users to specify the recording quality is quite important.