Concept implementation of Network.run_interactive() method

[jbaayen]

We are dealing with an application where we have some of our controllers implemented in Python. These need to read the current system state at every time step, compute control output, and feed the control output back into EPANET.

In this concept implementation, control is passed back to the caller subsequent to every time step using yield().

I don't like the idea of having many flavours of run() methods and would therefore like to use this pull request to open the discussion as to the design of a generic runner method, able to satisfy all relevant use cases.

[AbelHeinsbroek]

I see the added value of an interactive runloop using yield(). I also agree that too many run flavours would add unnecessary complexity.

The solution I propose is refactoring the module to have one single run method, that takes all run-relevant parameters:

interactive: Boolean        # if set to True, use yield()
duration: Integer              # if set to 0, calculate steady state
hydraulic_step: Integer    
report_step: Integer
...etc..

We can still keep the existing solve steady-state function as a convienience method, calling the main run method with certain set parameters.

[jbaayen]

Sounds good to me. Will refactor accordingly.