Simulator

Adds -Dsimulator to choose the simulator at runtime.

This trait adds an option for controlling the simulator at runtime.

If a user wants to add more simulators or simulators with different options, they should override the cliSimulatorMap with their chosen simulators.

If a user wants to change the default simulator, they should override defaultCliSimulator. Making this a None will require the user to always specify a simulator, i.e., there is no default.