Adds missed AltGr keycode
Adds missed AltGr keycode

`XK_ISO_Level3_Shift` is the code name for `AltGr`.

`NoSymbol` will help us to know when a keycode is meaningless or if it is unknown.

Also, i believe http://cgit.freedesktop.org/xorg/proto/xproto/tree/keysymdef.h is a better source to find keycodes. :-)
Arteris/node-x11,sidorares/node-x11,15lyfromsaturn/node-x11,15lyfromsaturn/node-x11,15lyfromsaturn/node-x11,Arteris/node-x11,sidorares/node-x11,sidorares/node-x11