Resolve "components/RobotUnitSimulation: Wrong timestamps in 'RobotState/Proprioception'-memory"

Fixes components/RobotUnitSimulation: Wrong timestamp... (#26 - closed)

Fixes the issue by setting the timestamps using the system's raw monotonic clock with armarx::rtNow(), as expected by the used RobotAPI code.

This is inconsistent with the rest of the RobotUnitSimulation-component, which exclusively uses the system's realtime or the time provided by a timeserver, but consistent with the timestamps set by the real-robot units.

I don't expect this to break anything (at least as long as the timeserver-functionality isn't used), as this change just adapts the behavior of the simulated RobotUnits to match the (correct) behavior of the real-robot RobotUnits.