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/environment.cpp

@@ -32,9 +32,7 @@
 #include "hostosinfo.h"
 
 #include <QDir>
-#include <QProcess>
 #include <QProcessEnvironment>
-#include <QString>
 #include <QCoreApplication>
 
 class SystemEnvironment : public Utils::Environment