CActor: Make Render() a non-const function

A few implementations of Render() contain const-casts nested within its
their call hierarchy to get around the fact that this function is marked
const. We can just make the member function non-const to allow removal
of these casts in follow up changes.

Runtime/Camera/CBallCamera.cpp

@@ -242,7 +242,7 @@ void CBallCamera::Reset(const zeus::CTransform& xf, CStateManager& mgr) {
   }
 }
 
-void CBallCamera::Render(const CStateManager& mgr) const {
+void CBallCamera::Render(CStateManager& mgr) {
   // Empty
 }