Env microphone

It acts as a microphone.
 * In "Speaker mode", it picks up sound and rebroadcasts it at a Speaker target. It ignores the Hears X spawnflags and does not fire the SoundLevel output.
 * In "Measuring mode", it measures the sound level at a Measure target and outputs the sound level as a value between 0 and 1. It only hears sounds that match the Hears X spawnflags.