0027957: Visualization, AIS_InteractiveContext - protect from displaying the same...

0027957: Visualization, AIS_InteractiveContext - protect from displaying the same AIS_InteractiveObject within multiple contexts

AIS_InteractiveContext methods adding object to the context now throws Standard_ProgramError exception
if object has been already displayed in another context.
AIS_InteractiveContext::Remove() now NULLifies context assigned to the object.

AIS_InteractiveContext now inherits from Standard_Transient instead of deprecated MMgt_TShared
and defines C++ destructor instead of method Delete().

AIS_InteractiveObject - undocumented property State() has been removed.
Undocumented property Users() has been moved to AIS_IdenticRelation.

Draw Harness command vclose now clear AIS_InteractiveContext content
before nullifying it to ensure that objects have been properly removed.

AIS_MultipleConnectedInteractive now overrides method ::SetContext()
to assign context for children objects.