Big Sur style toolbar icons

Author: sfsam

src/MacVim/MMVimController.m

@@ -1533,6 +1533,7 @@ - (void)addToolbarItemToDictionaryWithLabel:(NSString *)title
         img = [NSImage imageNamed:MMDefaultToolbarImageName];
     }
 
+    [img setTemplate:YES];
     [item setImage:img];
 
     [toolbarItemDict setObject:item forKey:title];