compositor,shell: move debug key code to core

The code for the key binding that triggers debug key bindings, that is,
the code that makes mod+SHIFT+SPACE work, used to live in shell.c. I
want to make the debug key bindings available in ivi-shell too, so this
code should be shared. Move it to core.

The code was originally introduced in
commit c509d2b1
so update the copyright in binding.c to reflect that.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Reviewed-by: Daniel Stone <daniels@collabora.com>