ui: Added plain text editing dialog to list boxes in project setup UI

* Added class QtTextEditDialog for displaying text content
* Added edit button to QtDirectoryListBox
* Replaced show files button dialog using QtProjectWizzardContentSourceList with QtTextEditDialog

src/lib_gui/qt/window/QtTextEditDialog.h

@@ -0,0 +1,34 @@
+#ifndef QT_TEXT_EDIT_DIALOG_H
+#define QT_TEXT_EDIT_DIALOG_H
+
+#include "qt/window/QtWindow.h"
+
+class QPlainTextEdit;
+
+class QtTextEditDialog
+	: public QtWindow
+{
+	Q_OBJECT
+
+public:
+	QtTextEditDialog(const QString& title, const QString& description, QWidget* parent = 0);
+
+	QSize sizeHint() const override;
+
+	void setText(const std::string& text);
+	std::string getText();
+
+	void setReadOnly(bool readOnly);
+
+protected:
+	void populateWindow(QWidget* widget) override;
+	void windowReady() override;
+
+private:
+	QString m_title;
+	QString m_description;
+
+	QPlainTextEdit* m_text;
+};
+
+#endif // QT_TEXT_EDIT_DIALOG_H