Out Canv: Generate OutputCanvasConfig callbacks also from a singleton class
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 7.1

Project: USACE ABQ 5.11: Output Canvas Items on Workspace views
http://cadswes2.colorado.edu/~philw/2017/CoeAbq5p11/proj.html

Architectural Preparation: Route OutputCanvasConfig change 
  notifications through a new singleton.

New module:
  Sim/OutputCanvasConfigMgr.hpp
  Sim/OutputCanvasConfigMgr.cpp

Notifications of changes to the OutputCanvasConfig made from the 
rwSettingTree-based editor are propagated to the OutputCanvasScene via 
RiverWare callbacks emitted from the OutputCanvasConfig. The 
OutputCanvasScene then routes some of those notifications to its 
contained graphics items, e.g. TeacupGfxItems.

With the upcoming enhancement, some object associated with the RiverWare 
Workspace Views (WorkspaceGfxScene instances) will need to receive these 
notifications from MULTIPLE OutputCanvasConfigs. Being that the CallbackData 
structures provided in the relevant callbacks contain a reference to the 
containing OutputCanvasConfig, we can simplify the registration of clients 
to receive those callbacks by routing the callbacks through a new singleton.

The new OutputCanvasConfigMgr singleton, just for the purpose of routing 
these callbacks was added. This is a "Root" subclass so that it can send 
out callbacks (to all entities that have registered to receive callbacks 
from this "Root" object). For now, this new manager class doesn't provide 
any other functionality. In particular, it doesn't keep track of the 
instantiated OutputCanvasConfig objects. (That is currently, effectively, 
being done by the Sim/cwOutputDeviceMgr object, for the corresponding 
OutputCanvasDevices).

I decided to also continue generating callbacks directly from 
OutputCanvasConfig.  Clients can receive change callbacks either from that 
object or the new OutputCanvasConfigMgr.  I did test the current GUI clients 
instead registering for the latter, but this commit reverses that text -- 
they are still registering for callbacks on the origin OutputCanvasConfig 
instance.

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