Use QWinOverlappedIoNotifier instead of QWinEventNotifier

The reasons of this change are following:

1) Implementation of QEventDispatcherWin32 has restrictions to
maximum quantity of QWinEvenNotifier instances in one thread.

Method QEventDispatcherWin32::registerEventNotifier() registers
the [MAXIMUM_WAIT_OBJECTS - 2] numbers of notifiers only. Where
the MAXIMUM_WAIT_OBJECTS that is equal to 64, since it is a part
of "Multiple-object Wait Functions" API:

http://msdn.microsoft.com/en-us/library/windows/desktop/ms687069%28v=vs.85%29.aspx

2) There is need to have three instances of QWinEventNotifier to
watch I/O events of each serial port.

It has limits to the maximum number of used serial ports and it
is [(MAXIMUM_WAIT_OBJECTS - 2) / 3] = 20 for the one thread.

3) Attempting to move or to resize a window of GUI application
lead to suspending of I/O events from serial port.

A long suspension can lead to overflowing of FIFO of device, so
the data can be lost.

All these shortcomings are resolved with QWinOverlappedIoNotifier,
which uses the "I/O Completion Ports" API:

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365198%28v=vs.85%29.aspx

Tested on Windows 8 with the virtual (com0com), on-board and
the USB (PL2303) serial ports.

Task-number: QTBUG-34946
Change-Id: I879d939f86c8dcde0fe21a8d6267e81152822aa4
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>