Fix exec icon location and bring it into XDG compliance

ksquirrel/sidebar/sq_categorybrowsermenu.cpp

@@ -514,7 +514,7 @@ void SQ_CategoryBrowserMenu::initIconMap()
     _icons->insert("kfm", SmallIcon("kfm"));
     _icons->insert("terminal", SmallIcon("terminal"));
     _icons->insert("txt", SmallIcon("text-plain"));
-    _icons->insert("exec", SmallIcon("exec"));
+    _icons->insert("exec", SmallIcon("application-x-executable"));
     _icons->insert("chardevice", SmallIcon("chardevice"));
 }