Show the non-rebindable shortcuts in preferences.

They can't be changed, but it will at least let people know that the key works for that command.
Currently they're just hard-coded. A more general solution would be possible, if there's
any chance that more non-rebindable hotkeys are needed.

This also removes Cmd+Shift+Q as a shortcut for Quit to Desktop on OSX.

data/core/hotkeys.cfg

@@ -347,12 +347,14 @@
     key=5
 [/hotkey]
 
+#ifndef APPLE
 [hotkey]
     command="quit-to-desktop"
     key="q"
     shift=yes
-    {IF_APPLE_CMD_ELSE_CTRL}
+    ctrl=yes
 [/hotkey]
+#endif
 
 [hotkey]
     command="editor-partial-undo"

src/hotkey/hotkey_item.cpp

@@ -476,6 +476,16 @@ std::string get_names(std::string id)
 			names.push_back(item->get_name());
 		}
 	}
+	
+	// These are hard-coded, non-rebindable hotkeys
+	if (id == "quit") {
+		names.push_back("escape");
+	}
+#ifdef __APPLE__
+	else if (id == "quit-to-desktop") {
+		names.push_back("cmd+q");
+	}
+#endif
 
 	return boost::algorithm::join(names, ", ");
 }