Major changes to Developer class interface

[pksohn]

This PR makes some major updates to the Developer class - not to the core functionality, but to the way it works with parameters, and most changes are basically to make the format consistent with the SqftProForma object. Addresses #11 and #22.

I took a crack at this but I'm not sure this is the best solution. See what you think. I could be convinced that we should leave some of the parameters out of the Developer object, like agents and buildings. It's hard to know what's the right separation between the parcel model functions and the core Developer object.

• Constructor: I brought a lot more parameters into this object than previously. This is largely due to bringing some functionality from the parcel model's utils.py into this module. See for example this function which has been brought inside the Developer object, along with the agents and buildings tables and other parameters.
• Add from_yaml, to_dict, and to_yaml functionalities.
• Major revamp of unit tests given new required parameters for instantiating the Developer object.