Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibHTML/Frame.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <LibHTML/DOM/Document.h>
+#include <SharedGraphics/Size.h>
+
+class Frame {
+public:
+    Frame();
+    ~Frame();
+
+    Document* document() { return m_document.ptr(); }
+    const Document* document() const { return m_document.ptr(); }
+
+    void set_document(Document*);
+
+    void layout();
+
+private:
+    RefPtr<StyledNode> generate_style_tree();
+
+    RefPtr<Document> m_document;
+    Size m_size;
+};