Initial Gamepad support

Adds initial ingame gamepad support to minetest.

Full Formspec support is not implemented yet and
can be added by a later change.

src/game.h

@@ -23,6 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "irrlichttypes_extrabloated.h"
 #include <string>
 #include "client/keys.h"
+#include "client/joystick_controller.h"
 #include "keycode.h"
 #include <list>
 
@@ -135,6 +136,8 @@ public:
 	virtual void step(float dtime) {}
 
 	virtual void clear() {}
+
+	JoystickController joystick;
 };
 
 class ChatBackend;  /* to avoid having to include chat.h */