This adds a QAPI schema for the properties of the input-* objects.

ui.json cannot be included in qom.json because the storage daemon can't
use it, so move GrabToggleKeys to common.json.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>