logic: Directory list box now restricts the user to select files, directories or both if required

* split QtDirectoryListBox and QtStringListBox
* renamed QtDirectoryListBox to QtPathListBox
* extracted QtListItemWidget class to own file
* renamed QtListItemWidget to QtListBoxItem
* added SelectionPolicyType to QtPathListBox to allow for specifying if selecting files, directories or both should be allowed.

src/lib_gui/qt/element/QtStringListBox.cpp

@@ -0,0 +1,37 @@
+#include "qt/element/QtStringListBox.h"
+
+#include <QListWidget>
+
+#include "qt/element/QtStringListBoxItem.h"
+
+QtStringListBox::QtStringListBox(QWidget *parent, const QString& listName)
+	: QtListBox(parent, listName)
+{
+}
+
+std::vector<std::wstring> QtStringListBox::getStrings()
+{
+	std::vector<std::wstring> strings;
+	for (int i = 0; i < m_list->count(); ++i)
+	{
+		QtListBoxItem* widget = dynamic_cast<QtListBoxItem*>(m_list->itemWidget(m_list->item(i)));
+		strings.push_back(widget->getText().toStdWString());
+	}
+	return strings;
+}
+
+void QtStringListBox::setStrings(const std::vector<std::wstring>& strings, bool readOnly)
+{
+	clear();
+
+	for (const std::wstring& str : strings)
+	{
+		QtListBoxItem* itemWidget = addListBoxItemWithText(QString::fromStdWString(str));
+		itemWidget->setReadOnly(readOnly);
+	}
+}
+
+QtListBoxItem* QtStringListBox::createListBoxItem(QListWidgetItem* item)
+{
+	return new QtStringListBoxItem(this, item);
+}