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/StyleSheet.cpp

@@ -0,0 +1,10 @@
+#include <LibHTML/CSS/StyleSheet.h>
+
+StyleSheet::StyleSheet(NonnullRefPtrVector<StyleRule>&& rules)
+    : m_rules(move(rules))
+{
+}
+
+StyleSheet::~StyleSheet()
+{
+}