[1149265] Main menu bar appears on top of Favorites menu in IE
This commit in effect reverts the CSS changes but keeps the fixes to I18N
and the user menu href.  Additionally:
- Remove FavoritesButton as that button was no longer used, and replace
  with FavoritesMenu.
- Remove some explicit zIndex settings and defer to the css defs in
  play due to the recent work for BZ 1144052.  Keep explicit zIndex for
  the MessageBar to ensure it gets precedence.
- Simplify menu bar interactions by clearing the message bar if the favs
  or user dropdowns are clicked on.