renderer updates (#191)

Big renderer refactor to remove some global state.
- Renderer no longer uses "global scene", but instead takes scene as parameter to functions
- Visibility is exposed, user can generate visibility for arbitrary camera and some exposed parameters
- Big changes in renderer can make user render code in high level interface not compatible with previous versions
- Fixed occlusion culling const correctness

Tests/Tests.cpp

@@ -126,7 +126,7 @@ void TestsRenderer::Load()
 		wiRenderer::GetDevice()->SetVSyncEnabled(true);
 		wiRenderer::SetToDrawGridHelper(false);
 		wiRenderer::SetTemporalAAEnabled(false);
-		wiRenderer::ClearWorld();
+		wiRenderer::ClearWorld(wiScene::GetScene());
 		wiScene::GetScene().weather = WeatherComponent();
 		this->ClearSprites();
 		this->ClearFonts();