iOS: implement 'close keyboard' gesture

Before this patch there were no way for the user to hide
the keyboard on iPhone for multi-line edit fields unless
the app had a separate button added for it. And even that
would be problematic since we scroll the screen (and
perhaps the button) to track the cursor.

This patch implements a gesture that resembles the 'hide
keyboard' gesture that UIScrollView implements on iOS 7.

Note that if you start the gesture inside the edit field,
you will start selecting text as well. This will also cause
the cursor to move and the screen to scroll. After some
testing and failing, it seems like we need to live with such
artifacts until we do get around to do the only sensible thing;
fix up how we do text selection on touch platforms. Working
around it becomes just to messy.

Change-Id: I1c0d9c88ff1f5430587a49591f165b9708e5dc60
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
iOS: send a Qt::Key_Return when the user hits done/enter

We need to send key events when the user hits enter, otherwise
there is no way to know when the user has 'confirmed' the
text he wrote. This is on par with how it's done for the
Android port.

Change-Id: I585d4198de24b0d251e5e0dd2956ce81b6483f82
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Setting QT_NO_DEBUG should not remove symbols

Removing symbols when defining QT_NO_DEBUG is a bad idea.
In this case it means that you can't compile corelib as a
release build and widgets as debug without getting an
undefined symbol.

Instead leave the method in the release build, but simply don't
call it.

Change-Id: I50426aefd62e82bccd933323aa0f67c6e5294961
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>