Support for sound projects

[dalelane]

I think we should be able to get sound projects working, in the same way that we've got image projects working with TensorFlow.js in an embedded WebView.

I tried to lay the groundwork for that in the way I added image support, so it should... in theory... be an incremental step on that.

The bit I'm not sure about is whether the browser running in the WebView will get access to the device microphone (I didn't try doing that for images - using the native AppInventor camera support and throwing the data at the webview instead).

It will be much more difficult if we can't do that, as all of the audio encoding stuff is in the JavaScript library - we won't want to re-invent the audio encoding on the Android/Java side, so the feasibility of doing sound project support will come down to whether we can let a WebView play with the phone microphone.

Assuming that is possible, the rest should be easy.... I think?
Worth a try at least.