QmlProject: Search for qmlviewer in configured Qt versions (if not found in $PATH)

If no 'qmlviewer' executable is found in the PATH, iterate through the
list of configured Qt versions and try to find a qmlviewer there. This
should help users configuring creator such to play with Qml.

Right now the first qmlviewer found in a Qt version is selected. A UI
to let the user select one explicitly was not possible any more (string
freeze).

This requires a dependency from QmlProjectManager to
Qt4ProjectManager.

Reviewed-by: dt

src/plugins/qt4projectmanager/qtversionmanager.cpp

@@ -749,6 +749,7 @@ void QtVersion::setQMakeCommand(const QString& qmakeCommand)
 #endif
     m_designerCommand.clear();
     m_linguistCommand.clear();
+    m_qmlviewerCommand.clear();
     m_uicCommand.clear();
     m_toolChainUpToDate = false;
     // TODO do i need to optimize this?
@@ -1202,6 +1203,22 @@ QString QtVersion::linguistCommand() const
     return m_linguistCommand;
 }
 
+QString QtVersion::qmlviewerCommand() const
+{
+    if (!isValid())
+        return QString();
+    if (m_qmlviewerCommand.isNull()) {
+#ifdef Q_OS_MAC
+        const QString qmlViewerName = QLatin1String("QMLViewer");
+#else
+        const QString qmlViewerName = QLatin1String("qmlviewer");
+#endif
+
+        m_qmlviewerCommand = findQtBinary(possibleGuiBinaries(qmlViewerName));
+    }
+    return m_qmlviewerCommand;
+}
+
 bool QtVersion::supportsTargetId(const QString &id) const
 {
     updateToolChainAndMkspec();