Help: Follow clicked links

This also adds a toolbar and a menu which allow you to
navigate back and forth through history ^)

Applications/Help/History.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+class History final {
+public:
+    void push(const StringView& history_item);
+    String current();
+
+    void go_back();
+    void go_forward();
+
+    bool can_go_back() { return m_current_history_item > 0; }
+    bool can_go_forward() { return m_current_history_item + 1 < m_items.size(); }
+
+    void clear();
+
+private:
+    Vector<String> m_items;
+    int m_current_history_item { -1 };
+};