This change should allow the usage of scancodes in the configuration
file.
When a VirtualKeyCode for glutin is not present, this should now allow
the user to use the scancodes instead. If the user specifiecs a key with
its scancode even though the key has a VirtualKeyCode, it should still
work.
The behavior of directly specifying a VirtualKeyCode should be unchanged
by this.
This fixes#1265.