intput-helper: client can say how many events emit
intpu-helper: change roundtrip for dispatch

creating another callback is useless
input-helper: events-test.c changed to comply with current changes

use socket for comunicating with display
input-helper: rewrite tests to comply with new API

also tests for emitting events has been deleted and will be
newly written in some of future commits
input-helper: include wayland-client-protocol.h into input-helper.h

Compiler cries without it
input-helper: check for display's error

After sync/roundtrips or at the end of client's main (client_free)