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]
#proj core
#branch UE4
#summary Removed header groups, removed some redundant includes and replaced with forward declarations. Fixed compilation errors.
[CL 2055361 by Mikolaj Sieluzycki in Main branch]
#proj core
#branch UE4
#summary Removed header groups, removed some redundant includes and replaced with forward declarations. Fixed compilation errors.
[CL 2054304 by Mikolaj Sieluzycki in Main branch]