Added Option-like MenuItem functionality

Set the Check property to True and the IconKey to the special value "OptMenuItem" to use it (As discused in #12)

I've found out that the checked MenuItems are displayed in a particular way, not passing by the cTheme class (DrawCheckMark Sub), so I have done the Option Drawing in the same way (trying to achieve a similar look).

You could test the Menu with your "MenuBarAndToolBar" example, by adding the following lines in the AddExtrMenuEntries Sub, in modMenuResources:
```VB
  Set SubMenuPar = MI.AddSubItem("Item6", "&Another SubMenu", "Document-Open")
    
    'three entries into the SubMenu (as children of 'Item6' of the above Code-Block) that are Option-like:
    SubMenuPar.AddSubItem "SubItem6-1", "Option &1", "OptMenuItem", , True
    SubMenuPar.AddSubItem "SubItem6-2", "Option &2", "OptMenuItem", , False
    SubMenuPar.AddSubItem "SubItem6-3", "Option &3", "OptMenuItem", , False
    'and just a few more:
    SubMenuPar.AddSubItem "SubItem6-4", "-", , , False
    SubMenuPar.AddSubItem "SubItem6-5", "Check &4", , , True

  Set SubMenuPar = MI.AddSubItem("Item7", "&Yet another SubMenu", "Edit-Copy")
    
    'three entries into the SubMenu (as children of 'Item7' of the above Code-Block) that are Option-like:
    SubMenuPar.AddSubItem "SubItem6-1", "Another Option &1", "OptMenuItem", , True
    SubMenuPar.AddSubItem "SubItem6-2", "Another Option &2", "OptMenuItem", , False
    SubMenuPar.AddSubItem "SubItem6-3", "Another Option &3", "OptMenuItem", , False
    'and just a few more:
    SubMenuPar.AddSubItem "SubItem6-4", "-", , , False
    SubMenuPar.AddSubItem "SubItem6-5", "Another Check &4", , , True
```
Greetings, Kbre.