Reworking management of Slot Dialogs, no longer via Open Object Dialogs
Bug Number: Related to 6006 (part 2 of 3)
Release notes (y/n): Yes
For Release Nums: 7.2

Open Slot Dialogs are no longer managed as child dialogs of their containing 
SimObj's Open Object Dialog (or Object Viewer).  So, now, closing an Open 
Object Dialog or the Object Viewer no longer also closes any Open Slot 
Dialogs which had been opened from that object dialog.

Note: This change was motivated by Gnats 6006 (part 2 of 3).  A simpler 
solution was devised within the Release_71 code base (now on the "Bug6006-71" 
branch) ... but that solution involves deleting and recreating Open Slot 
Dialogs when a SimObj is moved into our out from the Object Viewer.  That 
causes the loss of some Slot Dialog GUI state information, e.g. vertical 
scrollbar position and timestep cell selection.  We're not sure we want to 
use that change (for a 7.1 patch).

I had a couple failed attempts at moving the management of Slot Dialogs out 
from the OpenObjectDlg class (which also implements the new Object Viewer).
The solution I ended up pursuing was the elimination of the GUI/BaseRWDlg 
class's support for Parent Dialog / Child Dialog relationships.  That crazily 
complex (and very old) mechanism had been used primarily in these two ways:

   (1) OpenObjectDlg parenting of Open Slot Dialogs: 
      (a) Q3GUI/SlotQtDlg (most open slot dialogs)
      (b) Q3GUI/ListSlotDlg
      (c) Q3GUI/ScalarSlotDlg
      (d) Q3GUI/StatTableSlotDlg
      (e) QtUtils/MassBalSummaryDlg (NOT a BaseRWDlg, non-standard support)

   (2) SlotQtDlg parenting of slot configuration dialogs.

There are still some, now unused, Parent/Child-dialog mechanisms and data 
members in GUI/BaseRWDlg, but the public interface for that support has been 
removed (plus, some of the internal implementation).  This includes removal 
of these public methods:

   BaseRWDlg *openChildDlg (void *assocObj = NULL,
                            int  typeCode  = 0,
                            int  onlyOnce  = true,
                            int  dontOpen  = false);

   virtual BaseRWDlg *createChildDlg (void *assocObj, int typeCode);
   virtual void childDestroyedHandler (BaseRWDlg* child, void*);

Also, this module has been removed:
   GUI/SlotDialogManager.cpp

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