The lobby feature adds the possibility to lock a meeting and only allow people in after virtually knocking and going through formal approval

This commit refactors device selection (more heavily on iOS) to make it
consistent across platforms.

Due to its complexity I couldn't break out each step into separate commits,
apologies to the reviewer.

Changes made to device handling:

- speaker is always the default, regardless of the mode
- "Phone" shows as a selectable option, even in video call mode
- "Phone" is not displayed when wired headphones are present
- Shared device picker between iOS and Android
- Runtime device updates while the picker is open

Due to the difference in nature, the iOS and Android implementations are
completely different:

iOS: MPVolumeView is used, which allows us to place a button which will launch a
native route picker provided by iOS itself. This view is different depending on
the iOS version, with the iOS 11 version being more complete.

Android: A completely custom component is used, which displays a bottom sheet
with the device categories, not devices individually. This is akin to the sheet
in the builtin dialer.