Add new labels along the way

I want to introduce a new feature, to add new labels during the labeling process, not before.

If a dataset is large and unknown, usually the human operator can only infer labels exactly at the time perceiving it. Take some funny animal videos for example, it is largely unknown what makes people laugh before seeing it.

I use this feature in my personal project. Later I will include my screenshot of my implementation. As for this project, adding a new template is more helpful than merely creating new APIs.