Support absolute height, scrollbar, pageup, and pagedown

When the option object has the new height option set, a scrollbar will be visible if necessary. Scrolling via up, down, pageup, pagedown is supported along with all edge cases (if the selected value being transitioned from is above or below the visible items, or if we are going between the first and last items). 

Also fixed an issue with the mouse hover not actually affecting the selected item. This now follows how a standard select tag behaves, although it was not possible to force remove the hover style.