MS_CLIST_SHOWHIDEMENUITEM - new simplified service for the menus items' hiding/showing

git-svn-id: http://svn.miranda-ng.org/main/trunk@4318 1316c22d-e87f-b044-9b9b-93d7a3e3ba9c
various menu items quirks, simplifications & optimization

git-svn-id: http://svn.miranda-ng.org/main/trunk@4319 1316c22d-e87f-b044-9b9b-93d7a3e3ba9c