It mostly dealt with scrolling which we don't use. It also made mistakes
in some cases. Remove it and compute the coordinates directly in the
calling code.
Mouse wheel event handling has now been standardised and has broad
support. Use this event rather than the older, non-standard ones.
At the same time fix up support for horisontal mouse wheel events.
This commit moves all the input-related files from `core/`
to `core/input/`, and renames a couple as relevant
(input.js --> input/devices.js, keyboard.js --> input/util.js).
Samuel Mannehed
Pierre Ossman
zarmhast
Solly Ross