First part of render texture commit

Added NzContext::EnsureContext and NzContext::GetThreadContext
Added NzCube
Added NzRect::GetCenter
Added methods to send vectors to shaders
Added NzRenderer::SetViewport
Fixed NzRect::ExtendTo calculations
Fixed NzImage::Update checks with level > 0
No longer use glTexStorage when creating a texture to prevent a bug
NzBuffer's Lock and Unlock operations renamed to Map and Unmap
NzVector2/3/4 can now cast implicitly to a pointer
Optimized compilation time of String.hpp
Optimized normalisaton of quaternions
Optimized passing uniforms to shaders
Quaternion now automaticaly Normalize h
Removed macro definition of NAZARA_RENDERER_OPENGL from Renderer
Removed implicit cast from NzVector2/3/4 to NzString
Renamed nzBufferLock to nzBufferAccess
Renamed NzRenderTarget::CanActivate to IsValid

include/Nazara/Math/Rect.hpp

@@ -28,6 +28,8 @@ class NzRect
 		void ExtendTo(const NzVector2<T>& point);
 		void ExtendTo(const NzRect& rect);
 
+		NzVector2<T> GetCenter() const;
+
 		bool Intersect(const NzRect& rect) const;
 		bool Intersect(const NzRect& rect, NzRect& intersection) const;