Allow the camera to work without microphone access

[jschementi]

Right now we block the camera from being used until you grant microphone and camera access.

Instead, we could just require one of them, and respond accordingly:

• Just microphone access would show an audio-only recorder
• Just camera access would still record video, just without audio

In both cases, we'd have to show that we're missing the other permission, and provide a way to navigate to System Settings to enable it.