Allow users to dynamically adjust the assigned number of annotation instances

[orange0629]

In many cases, users can't finish all their assigned annotation task (e.g., 100 instances), but their remaining instances are still there and can't be reassigned, which is a waste of data. Meanwhile, some users may want to do more tasks than assigned, but then they have to create new accounts. Therefore, would it be possible to add a adjustable bar to the user interface, so that users could change the number of tasks anytime during their annotation.

Additionally, we could provide those functions to admins so that they could also adjust each user's task size, and therefore easily supervise the progress of annotation. This function is especially useful when we want all data in dataset get annotated (because we can't expect each user to finish all their jobs)

Lechen

[orange0629]

I am currently working on this issue so that we could get all our 2K instances in our dataset annotated. But I am still a new user of POTATO so please let me know if it's a bad idea.