* 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]
+ Refresh feature packs automatically when they change on disk.
+ Remove drag and drop and batch install, and replace it with a single button for installing in the details section.
+ Don't allow multiple copies of the dialog to be opened.
+ Fix a missing brush visible when resizing the dialog.
+ Fix an issue where brushes in the dialog could get deleted resulting in white images.
[CL 2385434 by Frank Fella in Main branch]
Moved starter content assets
Added mobile starter content assets
Starter content uses mobile starter content based on target platform
[CL 2372343 by bruce nesbit in Main branch]
