* fixed VisualizeTexture to show up items when using r.SetRes
* fixed compacting of RenderTarget pool to avoid performance issue happening over time
[CL 2052571 by Martin Mittring in Main branch]
#proj Engine
#branch UE4
#summary Fixed render target visualization when using r.screenpercentage
#change Make texture visualization code use the unscaled viewrect for its calculations
#change Give DrawRectangle function the size of the actual render target, not the scene rendertarget sizes
[CL 2047656 by Graeme Thornton in Main branch]
#proj core
#branch UE4
#summary Moved global variables to statics in FApp. Removed unused GUnclampedDeltaTime.
#codereview robert.manuszewski
[CL 2043034 by Mikolaj Sieluzycki in Main branch]
