project: replaced proxy with pre-cache

Removed proxy task and replaced with a true honest-to-god pre-cache for
footage. This footage is pre-cached to a sequence and therefore 100% ready
for use in it once the task is done.

app/render/backend/renderbackend.cpp

@@ -127,7 +127,7 @@ QFuture<QList<QByteArray> > RenderBackend::Hash(const QList<rational> &times)
       hasher.addData(reinterpret_cast<const char*>(&video_params_.format()), sizeof(PixelFormat::Format));
       hasher.addData(reinterpret_cast<const char*>(&render_mode_), sizeof(RenderMode::Mode));
 
-      copied_viewer_node_->Hash(hasher, t);
+      copied_viewer_node_->texture_input()->get_connected_node()->Hash(hasher, t);
 
       hashes.append(hasher.result());
     }