Refactor Cooldown handling in game

Currently we start a coroutine for the duel pair. This breaks "REVENGE". This is why we do now check if a cooldown is already running and if yes, we do not start a new one.

We should switch to individual cooldown handling. We could achieve this using the existing timer functionality in the userstate. We need to see how expensive the search for expired cooldowns gets when the player listgrows. Probably we can create a hybrid between timing and coroutines