use a system of deferred maps to keep track of frames that don't need to be rendered twice

Mostly used for exporting to ensure all frames get accounted for when being
sent from the renderer to the exporter through signals/slots.

app/render/backend/videorenderworker.cpp

@@ -30,7 +30,7 @@ NodeValueTable VideoRenderWorker::RenderInternal(const NodeDependency& path)
   if (frame_cache_->HasHash(hash)) {
     // We've already cached this hash, no need to continue
     emit HashAlreadyExists(path, hash);
-  } else if (frame_cache_->TryCache(hash)) {
+  } else if (frame_cache_->TryCache(path.in(), hash)) {
     // This hash is available for us to cache, start traversing graph
     value = ProcessNode(path);