Allow to run multiple bot programs simultaneous

[paulsonnentag]

• [x] add create bot function to spawn new bots
• [x] on step event iterate over each bot and execute it's programm one step further
• [ ] shuffle execution order to preserve fairness (has no effect right now, we'll deal with this later when bots can actually block each other)
• [x] destroy bot if it finished its script
• [ ] stop simulation state if all bots terminated (lead to buggy behaviour if no bots are there, simulation is paused immediately again)

12 has to be implemented first