Use pointer to Partition in Dialog_Base_Partition and derived classes (#759726)

Now use a pointer to the Partition object in Dialog_Base_Partition class
and derived classes, Dialog_Partition_{Copy,New,Resize_Move}.  This is
equivalent to how the Partition objects are managed in the Operation and
derived classes.

The Partition object is allocated and copy constructed in each derived
classes' set_data() method, called from each constructor and deallocated
in the destructors.  Considering the remaining Big 3, these classes are
never copy constructed or copy assigned so provide private definitions
and no implementations so the compiler enforces this.

Bug 759726 - Implement Partition object polymorphism