added update next event, wrote more tests and moved max_simulation_time to __init__ of simulation
added update next event, wrote more tests and moved max_simulation_time to __init__ of simulation

Lieke19/ASQ,geraintpalmer/ASQ,geraintpalmer/QNetSim,geraintpalmer/Ciw,geraintpalmer/SimulatingAQingNetwork,CiwPython/Ciw