ui: Show news sent with update check on start screen

* News are passed as JSON string, containing an array of news items.
* Each news item has version and content (html).
* Items can be filtered by min/max version, OS and license. The first item that fits is used.
* Items can be important, which highlights the news box.
* News are not shown if older than 5 days.

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src/lib_gui/qt/element/QtTextEdit.h

@@ -0,0 +1,23 @@
+#ifndef QT_TEXT_EDIT_H
+#define QT_TEXT_EDIT_H
+
+#include <QTextBrowser>
+
+class QtTextEdit
+	: public QTextBrowser
+{
+	Q_OBJECT
+
+public:
+	QtTextEdit(QWidget* parent = nullptr);
+
+	void setViewportMargins(int left, int top, int right, int bottom);
+
+signals:
+	void focus();
+
+protected:
+	void focusInEvent(QFocusEvent* event);
+};
+
+#endif // QT_TEXT_EDIT_H