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/CSS/StyleDeclaration.cpp

@@ -0,0 +1,11 @@
+#include <LibHTML/CSS/StyleDeclaration.h>
+
+StyleDeclaration::StyleDeclaration(const String& property_name, NonnullRefPtr<StyleValue>&& value)
+    : m_property_name(property_name)
+    , m_value(move(value))
+{
+}
+
+StyleDeclaration::~StyleDeclaration()
+{
+}