Add optional parameters to scenarios

[geegaz]

To be able to make more varied scenarios, here's a list of existing parameters that should be exposed in scenario files as optional parameters:

For Belts (accessible after initialization through input_belt and output_belt in Machines):

• size (default = number of tiles, defined by the environment)

For InputMachines

• infinite (default = false)
• create_order (default = 0, values = 0,1,2) - invalid values are treated as 0
• create_time (default = 0, values = 0,1) - invalid values are treated as 0
• time_step (default = 15)