Long running / crashing kernels

[ptheywood]

Known combinations of parameters that led to long running cells that may have crashed the instancehub images:

    [cudaSimulation, pop_tracker] = initialise_simulation(num_prey = 10, num_predators = 100, num_grass = 0, seed = 64)
    cudaSimulation.SimulationConfig().steps = 800

This leads to death of all predators, so exponential growth of prey, and long runing kernels.

• Add an Exit condition, based on either all predators dieing or populations hitting a cap.