Introduce LFIDBearer, a Class for menu bearing UI that offers IDs to menus

Move menu code from scroll list into there
Separate out interface for getting IDs

No longer bother with the focus manager, for menus where not necessary,
this ensures that if focus suddenly changes, it won't break menu UX flow.

Clean up all the static functions by using new static class functions

indra/llui/llscrolllistctrl.cpp

@@ -59,8 +59,6 @@
 
 static LLRegisterWidget<LLScrollListCtrl> r("scroll_list");
 
-std::vector<LLMenuGL*> LLScrollListCtrl::sMenus = {}; // List menus that recur, such as general avatars or groups menus
-
 // local structures & classes.
 struct SortScrollListItem
 {
@@ -314,7 +312,7 @@ std::vector<LLScrollListItem*> LLScrollListCtrl::getAllSelected() const
 	return ret;
 }
 
-uuid_vec_t LLScrollListCtrl::getSelectedIDs()
+uuid_vec_t LLScrollListCtrl::getSelectedIDs() const
 {
 	uuid_vec_t ids;
 	if (!getCanSelect()) return ids;
@@ -1813,10 +1811,7 @@ BOOL LLScrollListCtrl::handleRightMouseDown(S32 x, S32 y, MASK mask)
 		if (col->mHeader && col->mHeader->getRect().pointInRect(x,y)) // Right clicking a column header shouldn't bring up a menu
 			return FALSE;
 	}
-	gFocusMgr.setKeyboardFocus(this); // Menu listeners rely on this
-	mPopupMenu->buildDrawLabels();
-	mPopupMenu->updateParent(LLMenuGL::sMenuContainer);
-	LLMenuGL::showPopup(this, mPopupMenu, x, y);
+	showMenu(this, mPopupMenu, x, y);
 	return TRUE;
 }