Clean headers in Utils.

Forward-declare QGraphicsOpacityEffect in DetailsButton,
QProcessEnvironment in Environment, QFileInfo in fileutils,
QUrl in IWelcomePage, FancyLineEdit in PathChooser and
remove unneeded headers.

Change-Id: I7d5f273530dd2059bbdaf0899f0a3bc7e49e8482
Reviewed-by: hjk <hjk121@nokiamail.com>

src/libs/utils/flowlayout.cpp

@@ -29,8 +29,6 @@
 
 #include "flowlayout.h"
 
-#include <QRect>
-#include <QWidgetItem>
 #include <QWidget>
 
 using namespace Utils;