Auto iterate through configuration inputs

Allows user to map all inputs seamlessly without having to
click on each button.

Also increased button timeout to 5 seconds from 1.5 due to pita.

Motion controls are not included since they will be special cases.
This looks kind of confusing, especially since incrementing an iterator past the end would be an undefined behavior. It can't happen in this case because we're sure btn is present in control_buttons, but it would be great if the code could be restructured in a less confusing way.