ONTRA-2948 Scrolling on Mac is all-or-nothing type of deal, where going ...

...down one notch takes you almost or completely to the bottom of any pane regardless of height and velocity. This will cap the velocity at a speed limit, suggested at 5 (this seemed to be the about the fastest a Windows 7 machine would scroll on Chrome and Firefox, where as a somewhat quick stroke on Mac trackpad would be ~130 velocity). Capping at 5 dramatically increases the shot-to-the-moon effect. Also adding a retention on the initial scrollSpeed delta if javascript reports a platform of MacIntel or MacPPC.