Fix module menu alignment and hover in Internet Explorer
In Internet Explorer, labels in the module menu are not aligned the same as other browsers due to a collapsing span on the menu icons. Also, Internet Explorer 6 does not support the hover attribute on list elements.
To fix this, I've changed the icons to float left which allows IE and other browsers to give them a consistent width (regardless of icon size) and preserve the alignment in all browsers. For the hover, I've used a CSS selector within prototype to add and remove a hover class on mouseenter and mouseleave. These events are only available in IE, but thats fine since IE is our target.
(issue imported from #M7598)