Made resource loading fail gracefully when a resource can't be loaded. Resources should now throw exceptions in their constuctor if the resource can't be loaded. This will result in ResourceManager::Load returning null.

src/Engine/Rendering/RawModel.cpp

@@ -8,7 +8,7 @@ RawModel::RawModel(std::string fileName)
 	if (scene == nullptr) {
 		LOG_ERROR("Failed to load model \"%s\"", fileName.c_str());
 		LOG_ERROR("Assimp error: %s", importer.GetErrorString());
-		return;
+        throw std::runtime_error("Failed to open model file.");
 	}
 
 	auto m = scene->mRootNode->mTransformation;