UETOOL-213 - Minimize Slate FString -> FText conversion (remove SLATE_TEXT_ATTRIBUTE)
This fixes any editor/engine specific code that was passing text to Slate as FString rather than FText.
[CL 2399803 by Jamie Dale in Main branch]
#TTP 349472 - UE4: Animaiton: Skeleton Tree should always have option to display retargeting information, in all tabs.
[CL 2333224 by Martin Wilson 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]
Animation - Add AnimationRelative retarget mode which applies translation similar to an additive animation.
#codereview Lina.Halper
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Integrated using branch Ue4-To-UE4-Fortnite-Simple (reversed) of change#2321428 by Jaren.Peterson on 2014/10/07 12:27:44.
[CL 2325869 by Jaren Peterson in Main branch]
#TTP 344032 - skeletal mesh interface: new sockets are not automatically selected after their creation (which can make the socket creation workflow a little less than ideal when making large numbers of them at once)
[CL 2308691 by Martin Wilson in Main branch]
