Move voice config to 00voice.rpy.

In general, config variables that only touch common/ should only
exist in common/.
Initial run at updating the changelog.
Revert "Move voice config to 00voice.rpy."

This reverts commit e612e2a168822e1e0804b825953808fefb83df7d.
Make reduce_volume_in_voice opt-in by creators.

This will break existing games, by changing the volumes in a way
creators will not expect. Let's make this opt in across the board.

Removed it from the various templates since voice stuff is pretty
rarely used, and shouldn't required attention from a new user.