LibWeb: Start implementing basic JavaScript DOM bindings

This patch introduces the Wrapper and Wrappable classes.

Node now inherits from Wrappable, and can be wrapped in a GC-allocated
Bindings::NodeWrapper object. The only property we expose right now is
the very simple nodeName property.

When a Document's JS::Interpreter is first instantiated, we add a
"document" property with a DocumentWrapper object to the global object.

This is pretty cool! :^)

Libraries/LibWeb/Bindings/DocumentWrapper.cpp

@@ -0,0 +1,29 @@
+#include <LibJS/PrimitiveString.h>
+#include <LibJS/Value.h>
+#include <LibWeb/Bindings/DocumentWrapper.h>
+#include <LibWeb/DOM/Document.h>
+
+namespace Web {
+namespace Bindings {
+
+DocumentWrapper::DocumentWrapper(Document& document)
+    : NodeWrapper(document)
+{
+}
+
+DocumentWrapper::~DocumentWrapper()
+{
+}
+
+Document& DocumentWrapper::node()
+{
+    return static_cast<Document&>(NodeWrapper::node());
+}
+
+const Document& DocumentWrapper::node() const
+{
+    return static_cast<const Document&>(NodeWrapper::node());
+}
+
+}
+}