Making SimpleCrop PyMT compatibible

[cpritcha]

In the Main.f03 of simplecrop you can see that models mutate state used by other models in the rate and integ phases. This makes adopting PyMTs single update method and getter/setter interface more difficult because each model wants to change each others state part way through their respective update methods (assuming that the rate and integ methods are inside the update method). We could get around this by more closing the following a Moore machine model (add a separate output method or using getters at the beginning of the step) instead of just an update method (the Mealy machine model). Following a Moore machine model would result in a slightly different simulation but it would also ensure that each component is receiving messages from its current time slice.

Since SimpleCrop has a CLI it would benefit from some multi-step optimizations from coupled models where the model relationships form a DAG (if the coupled model is a DAG then data across all time-steps to the SimpleCrop model at once). Should be as easy as providing support for giving a years worth of irrigation and weather data to the model.