Slate Widget was failing, because of missing Slate dependencies. Testing introduced a couple of problems which all was fixed by this CL:
1. I introduced AdditionalDependencies in .uproject file and change "Add Code To Project..." procedure to fill this array if needed. UBT reads this field and builds the project with required modules. Needed for Slate classes.
2. Changed UHT to #include missing headers in generated.h files if it was missing an include for it's super class. It was causing problems if we were trying to add a subclass of BrushShape -- BrushShape.h didn't have #include "Brush.h" and UBrushShape was inheriting from UBrush.
3. Above problems also occured for Slate classes, but not all of them was UCLASSes, so I had to fixed that manually.
4. "Add Code To Project..." functionality was not invalidating UBT makefiles, which lead to omitting new source files during hot-reloading (even thought it was reporting a success). This change also should improve a bit performance, cause right now there is no "gathering" step -- there is only invalidate step which is a lot quicker.
5. Fixed "Selected Class Source" link to source class in Slate Widget and Slate Widget Style class.
#codereview Robert.Manuszewski
[CL 2481488 by Jaroslaw Palczynski in Main branch]
