Improve reproducability of simulations

[brettle]

At the moment, WebotsSimulator and the controller synchonize time via NetworkTables but the actual sim values are sent via the halsim WebSockets server. As a result, there is a race condition between the 2 and the simulator might step forward before receiveing all of the new sim actuator values or the robot might step forward before receiving all of the sim sensor values.

One option would be moving the time sync back to halsim if we can avoid the hangs we were seeing in an earlier implementation. Those might be avoidable if we ensure that none of the processing happens directly in the callbacks but is instead queued for processing in a separate thread.

[brettle]

Fixed by PR #114.