Hooked up RLVaTopLevelMenu setting so it actually works.

Changes to llviewermenu.cpp are better viewed without space changes
^Put together both RLVa Embedded and RLVa Main menus while building Advanced menu, labeling them RLVa; once the advanced menu is built and added to MenuBar, rlvMenuToggleVisible() is called.
Added onChangedMenuLevel() to rlvcommon.cpp
Added rlvMenuToggleVisible(), tweaked to only perform necessary operations for now, other parts left commented out for future use.
Removed menu visibility handling from RlvHandler::setEnabled()

NOTE: RLVa has only been updated in pertinent areas, from what I can tell we are a bit behind in other places, too.