Touchups to scroll list building

Moved handling of mouse_wheel_opaque and menu_file to setScrollListParameters
Removed setToolTip block from LLScrollListCtrl::fromXML since setToolTip lives inside of LLView::initFromXML which is called by LLUICtrl::initFromXML which was already called at this point
Added support for building columns from xml with relative_width which is synonymous with relwidth
Fixed namelist columns not supporting dynamic_width in xml (dynamicwidth is only acceptable in older xmls)