Slate: Moved TestSuite and ColorPicker into new module AppFramework

The AppFramework module is intended to be used for compound widgets and UI related classes that are too specific (not basic enough) for Slate, but also not Editor specific (reusable in non-Editor applications and games). The test suite has been moved in its entirety for now, but core widget specific test classes will eventually be split off and moved back into Slate, so that they can live alongside of their corresponding widgets.

Other changes:
- moved to "include what you use" scheme for SColorPicker
- broke out color picker related widgets that may be reusable
- added forward declarations to reduce header include dependencies

#CodeReview: saul.abreu

[CL 2275496 by Max Preussner in Main branch]

Engine/Source/Editor/IntroTutorials/Private/STutorialEditableText.cpp

@@ -5,9 +5,12 @@
 #include "IDocumentation.h"
 #include "ISourceCodeAccessModule.h"
 #include "ContentBrowserModule.h"
+#include "SColorPicker.h"
+
 
 #define LOCTEXT_NAMESPACE "STutorialEditableText"
 
+
 namespace TutorialTextHelpers
 {