Merge in code from private repos into public repos

[dplarson]

This issue is mostly to help organize information as I merge in code (via multiple PRs) that was developed in private git repos into the Solar Arbiter's public git repos. This was a mistake on my part from trying to juggle code development with some company IT/infrastructure specific work. For the benefit of everyone (current and future contributors), I'll be pulling code out from those private git repos and creating multiple new PRs to merge the code into the public repos in steps (rather than creating one massive PR).

List of code modules, associated issues and corresponding PRs:

• add load as a variable (which will be treated as distinct from net_load):
  • issue: Add variable type for gross load #787
  • PR: datamodel: add load as an allowed variable #806
  • status: under review
• add support for defining a wind power plant site in the data model:
  • issue: Add WindPowerPlant subclass of Site in DataModel #785
  • PR:
• expand discussions of metrics and their interpretation in the Metrics page of the SFA website:
  • issue: Expand discussions of metrics and their interpretation SolarArbiter.github.io#222
  • PR: PR: metrics: add interpretations of error metrics SolarArbiter.github.io#225
  • status: under review
• expand examples of using the SFA for forecast trials to better reflect current practices and use cases (based on stakeholder feedback):
  • issue: Expand examples of using the SFA for forecast trials SolarArbiter.github.io#223
  • PR: Improve forecast trial docs SolarArbiter.github.io#224
  • status: under review
• add support for uploading wind speed, wind power and load data (observations and forecasts):
  • issue: Add support for uploading wind and load data #805
  • PR:
• add support for generating reports with wind and load forecast evaluation results:
  • issue: Support wind power and load explicitly in reports #789
  • PR: