A spell alert has a property called "pulse". Most spell alerts enable pulse to make the alert stand out - that's why we have alerts in the first place.

But some rare alerts, usually intermediate alert, are not meant to be a call to action. For example:

• Fire Mages have a Heating Up state before triggering Hot Streak, only Hot Streak is really important
• Enhancement Shamans can stack Maelstrom Weapon up to 5 stacks, but only the 5th stack is really important

To go further with the 'very important vs. less important' idea, the spell alert sound should not be played when the spell alert is not pulsing.

Implemented in #254.