Add Basic Model Interface

[lrntct]

Implement a Basic Model Interface. This required a large code refactoring. In addition to the BMI, the changes include:

• Most classes are no longer depending on the GIS interface.
• Use dependency injection and factory function to build the Simulation class.
• SWMM is no longer integrated in the code base. Itzi now depends on pyswmm for the drainage module.
• The Cython code can now be run in either float or double
• The hydrology module now uses m/s units internally. Unit conversions are made on import/export
• Green-Ampt infiltration is tested against a high precision analytic solution (fix #89)