Fix some errors with meshrenderer moving to engine that gemini didnt have time to fix

Will have to resync how to load more meshes. Probably need a command to do it but for now not needed.

Juliet/include/Core/Application/ApplicationManager.h

@@ -8,5 +8,6 @@ namespace Juliet
 {
     enum class JulietInit_Flags : uint8;
 
+    struct Arena;
     extern JULIET_API void StartApplication(IApplication& app, JulietInit_Flags flags);
 } // namespace Juliet