Keeping worse bots

There are a few bots doing worse than sample.SittingDuck, but we should keep them, at least not removing them in one step. 1. Removing a lot of bots in roborumble in a short period of time disables the comparation between different versions of every bot in APS, survival, PWIN, etc. As they all depends highly on the distribution of the participants. Doing so makes the recorded APS in version history completely useless. 2. They are a great indicator of whether your bot has some serious bug that happens rarely. Therefore we DO need enough weak bots. 3. They don't waste time in roborumble as they die too fast, making a battle almost done immediately.