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.cpp

@@ -0,0 +1,18 @@
+#include "QtTextEdit.h"
+
+QtTextEdit::QtTextEdit(QWidget* parent)
+	: QTextBrowser(parent)
+{
+	document()->setDefaultStyleSheet("a { color: #007AC2; }");
+}
+
+void QtTextEdit::setViewportMargins(int left, int top, int right, int bottom)
+{
+	QAbstractScrollArea::setViewportMargins(left, top, right, bottom);
+}
+
+void QtTextEdit::focusInEvent(QFocusEvent* event)
+{
+	emit focus();
+	QTextBrowser::focusInEvent(event);
+}