restructure and add ipi texs

ws2019/ipi/uebungen/cpp_headers/DeQueue.hh

@@ -0,0 +1,12 @@
+template<class T>
+class DeQueue : private DLList<T> {
+public :
+  // Default-Konstruktoren + Zuweisung ok
+  bool empty ();
+  void push_front (T t);
+  void push_back (T t);
+  T pop_front ();
+  T pop_back ();
+  T front ();
+  T back ();
+} ;