Proxy,Mipmapping: partly unbreak, partly break existing code, which was using strange rounding methods.
be explicit each time you downscale a rectangle: do you wand the largest enclosed or the smallest enclosing rectangle?
rounding dimensions to the closest power of two makes no sense (kit make sense within OpenGL, where only POT textures were allowed, but not here)
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Engine/EffectInstance.cpp
	Engine/ViewerInstance.cpp
	Gui/ViewerGL.cpp