Fixes TTP 335869 - UE4: RENDERING: CRITICAL: EDITOR: CRASH: Occurs when launching mobile preview on the StarterMap using the Asus UX31 Sandy Bridge Ultrabook
[CL 2119491 by Graeme Thornton in Main branch]
#ttp 331829 - Mobile Preview in Editor
#proj Engine
#branch UE4
#summary First pass of changes to remove GRHIFeatureLevel, allowing for multiple scenes with different feature levels to exist. First step towards dynamic mobile preview in the editor.
#change Added GMaxRHIFeature level which contains the highest supported feature level on this machine
#change Added a cvar "r.FeatureLevelPreview" which, when set to 1, enables a feature level selection in the quick settings menu. Not wired up to anything at the minute
#change Added a feature level variable to FScene, which is currently initialized to whatever GRHIFeatureLevel is. Accessed with GetFeatureLevel()
#change Added a helper accessor GetFeatureLevel() to FSceneView which gets the feature level from the relevant scene. Purely to reduce the amount of typing needed to get to a feature level
#change Many changes across the renderer to try and read the current feature level from the view or scene. Not everything is done yet, but this is almost all of the "easy" stuff. As there is still just a global feature level in the engine, nothing should change.
[CL 2066905 by Graeme Thornton in Main branch]
#proj Engine
#branch UE4
#summary Reposition texture visualization display when camera safe zone black bars are enabled
[CL 2065537 by Graeme Thornton in Main branch]
* 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]
