Make submenus easier to access

[bradyvercher]

The hoverTimeout option allows for setting a delay before submenus disappear, but a better approach would be to do something like what Amazon does to keep it snappy.

• http://www.asktog.com/columns/022DesignedToGiveFitts.html (Question 6)
• http://bjk5.com/post/44698559168/breaking-down-amazons-mega-dropdown
• http://thomaspark.co/2011/10/making-menus-escapable/
• https://css-tricks.com/dropdown-menus-with-more-forgiving-mouse-movement-paths/