Server memory and Task handling

[gbtami]

I collect some links here to get better overview about this topic.

The Heisenbug lurking in your async code
https://docs.python.org/3/library/asyncio-task.html#creating-tasks
https://discuss.python.org/t/whats-up-with-garbage-collected-asyncio-task-objects/29686/2

https://docs.python.org/3/library/gc.html

I find that abandon_game_task in user.py and wsr.py is completely mishandled. It should be a dict of game, task pairs.