data: Option to run only C/C++ preprocessor when indexing (issue 297)

* Added as checkbox to indexing start dialog
* Only shown for C/C++ projects
* Files will be marked incomplete

src/lib_gui/qt/element/QtHelpButton.cpp

@@ -0,0 +1,33 @@
+#include "qt/element/QtHelpButton.h"
+
+#include <QMessageBox>
+
+#include "utility/ResourcePaths.h"
+
+QtHelpButton::QtHelpButton(const QString& helpText, QWidget* parent)
+	: QtIconButton(
+		(ResourcePaths::getGuiPath() + "window/help.png").c_str(),
+		(ResourcePaths::getGuiPath() + "window/help_hover.png").c_str(),
+		parent)
+	, m_helpText(helpText)
+{
+	setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
+	setAttribute(Qt::WA_LayoutUsesWidgetRect); // fixes layouting on Mac
+	setMouseTracking(true);
+
+	setToolTip("help");
+
+	leaveEvent(nullptr);
+
+	connect(this, SIGNAL(clicked()), this, SLOT(handleHelpPress()));
+}
+
+void QtHelpButton::handleHelpPress()
+{
+	QMessageBox msgBox;
+	msgBox.setText("Help");
+	msgBox.setInformativeText(m_helpText);
+	msgBox.setStandardButtons(QMessageBox::Ok);
+	msgBox.setDefaultButton(QMessageBox::Ok);
+	msgBox.exec();
+}