Fix exec icon location and bring it into XDG compliance

diff --git a/src/autostart.cpp b/src/autostart.cpp
index 2c15469..30ac0c0 100644
--- a/src/autostart.cpp
+++ b/src/autostart.cpp
@@ -250,7 +250,7 @@
     ksc.setGroup("Desktop Entry");
     ksc.writeEntry("Encoding","UTF-8");
     ksc.writeEntry("Exec",service->exec());
-    ksc.writeEntry("Icon","exec");
+    ksc.writeEntry("Icon","application-x-executable");
     ksc.writeEntry("Path","");
     ksc.writeEntry("Terminal",false);
     ksc.writeEntry("Type","Application");