Send Audio files shared to element as m.audio instead of m.file

**Describe the bug**

When sharing an audio file to element, the message sent is treated as m.file, a generic file message, instead of m.audio, an audio message.

**To Reproduce**

Share an aduio file from an external app to element. Note that the element web audio player does not function, since it doesn't recognize the message type as m.audio.

**Expected behavior**

An audio message would be recognized as such in element web, triggering the HTML5 audio player in the UI. (Incidentally, element-android and element-iOS should both have audio players, but that's a separate issue. They should also both have audio recording features, but that is yet another issue. And I'm too tired to fill out five more issues right now.)

**Smartphone (please complete the following information):**
Android and iOS devices both seem to have this bug.