Whitespace
OpenALBackend: Log the actual backend device name
OpenALBackend: Always initialize the EFX extension
Remove enableEAX parameter from audio::init
CMake: Include EFX in config summary
OpenALSource: Remove obsolete TODO
Variable name
OpenALBackend: Implement environment effects

The only environment actually used in the game (alley.aef) isn't all
that interesting, but the other .aef files shipped with the game are
interesting.
Don't reset the audio system when toggling EAX
Remove audio::Backend::setRoomRolloffFactor()

This was always set to the same value as the normal rolloff factor so
there is no point in having two separate functions.
Mark single argument constructor as explicit
Use ARX_DEAD_CODE() as optimizer hint
audio: Add init parameter to select output device
Add config option for the audio output device
audio: Change unknown device error into warning
audio: Add function to query available devices
Remove unused audio::Backend::updateDeferred()
Add size() member function to rectangle
Replace audio backend in menu with audio device

We currently only have one backend (OpenAL) and that is unlikely to
change soon.