godot-demos/2018/09-11-input-actions-remapping lack of gamepad support

[TheMikirog]

I'm submitting a...

• Bug report.
• Feature request.

What is the current behavior?
Using a gamepad to assign buttons / axis crashes the program.

What is the expected behavior?
The program should detect the button press on gamepad and then I should be able to use that button during the game.

Tell us the steps to reproduce the bug, and if possible share a minimal demo of the problem.

1. Run the program
2. Bring up the Input mapper with ESC
3. Select Custom profile
4. Press any Change button
5. Press a button / axis on any gamepad
6. The game crashes

Other information
Errors:
Invalid get index 'scancode' (on base: 'InputEventJoypadButton'). (pressing a button)
Invalid get index 'scancode' (on base: 'InputEventJoypadMotion'). (using an analog stick)

The program expects a keyboard input and assumes that we're passing input events that contain the scancode variable, which doesn't exist on gamepad. Instead, button_index should be used for buttons. Analog sticks however are a bit tricky, because one axis represents both directions, so we need to use both axis and value used.