Allow voice message playback to continue on locked phone, and integrate with media controls

[jakewb-b]

As a user playing a voice message on Element on Android
I can lock my phone and continue to play the voice message
So that I can listen to the voice message with my phone locked

As a user playing a voice message on Element on Android
I can control voice message playback from the lock screen
So that I can easily pause and play the voice message with my phone locked

[RayBB]

This is related to the discussion here #3664

I also would love to be able to listen to messages when my phone is locked. Especially if they would play one after another.