Code review comment for lp://qastaging/~marcustomlinson/indicator-sound/fix-scroll-wheel-step-sizes

I agree that there are two bugs here wrt (1) inconsistent scrolling and (2) no smaller steps being available for raising/lowering the volume, but we should fix these by bringing the code into agreement with the existing spec. See https://bugs.launchpad.net/indicator-sound/+bug/1091142 and https://bugs.launchpad.net/indicator-sound/+bug/1226931/comments/2