Add NFP for DefaultConstructionSet

[kbenne]

Pull request overview

Adds the NFP design document for native DefaultConstructionSet support in EnergyPlus, proposing building and space level default construction assignments to reduce repeated surface construction inputs and facilitate OpenStudio alignment.

[RKStrand]

I get the desire to provide something that makes E+ and OS closer to the same thing and don't really have any problems with this. As long as users can still do what they have done previously--still define a construction for every surface as part of that object (which you propose is still going to be allowed), I don't have anything against moving this forward. While it doesn't add new functionality to E+, there could be some potential benefits to having this option. The slight downside is that for those who read their IDF directly, it's one more layer of search that one might have to go through to find the construction information, but presumably users taking advantage of this proposed new feature will trade that for a more universal definition of construction that simplifies the input and changes.