* Multicast delegate Add* calls now return FDelegateHandles, and Remove* calls are now all deprecated, except for a new Remove function which takes a FDelegateHandle.
* New FConsoleManager::RegisterConsoleVariableSink_Handle and UnregisterConsoleVariableSink_Handle functions which work in terms of FConsoleVariableSinkHandle.
* Timer calls which don't take FTimerHandles are deprecated.
* FTicker::AddTicker now returns an FDelegateHandle and is removed by an overloaded Remove function.
* DEFINE_ONLINE_DELEGATE* macros now define _Handle variants of the Add/Remove functions which return/take handles.
* Various other handle-based registration changes.
* Some unity build fixes.
* Some simplification of delegate code.
* Fixes for lots of existing code to use handle-based registration and unregistration.
#codereview robert.manuszewski
[CL 2400883 by Steve Robb in Main branch]
#jira UE-1378 - EDITOR: Layers: Visibilty icon different and on opposite side compared to Scene Outliner
[CL 2377233 by Richard TalbotWatkin in Main branch]
* Moved Slate.h into SlateBasics.h and began shifting less commonly used headers into SlateExtras.h.
* Slate.h now simply includes SlateBasics.h and SlateExtras.h.
* Slate.h includes a deprecated warning now to indicate that SlateBasics.h + specific includes should be used instead.
* Moved dozens of inlined functions using Slate widgets into .cpp files to avoid header dependencies.
* All code samples now include SlateBasics.h and SlateExtras.h so future shifts will not break most those projects, but not trigger the deprecation warning of including Slate.h.
#BUN
[CL 2329610 by Wes Hunt in Main branch]
