Play a sound for Granite.MessageDialog

## Problem

Many users may react slowly or not be able to immediately notice an error popup. The user has to be staring at their to notice a popup, which is pretty bad if it is a critical error.

## Proposal

Gala should play a crisp 'dunn' sound effect when a Granite.MessageDialogue with an error appears, and for when a Granite error views appears.
This should be done on an opt-in basis to avoid accidentally confusing users.
I'd also suggest adding a lighter sound effect for authentication popups.

tl;dr
Error views and granite error dialogues should have unique audio cues

## Prior Art

_Maybe I'll add some later_