Fetch egrid and avert variables in calculate route

[ryanhu021]

Description
Before being able to evaluate or construct any formulas in our /calculate API route, we must fetch the corresponding eGRID and AVERT variables from MongoDB. We can do this by calling the getEgridRecordByKey() and getAvertRecordByKey() functions. Once both records are fetched, we should add all variables in the to the FormulaParser by calling

Acceptance Criteria
The /calculate route is extended to retrieve eGRID and AVERT records based on the input parameters. Variables are added to the FormulaParser in preparation for adding formulas.

Steps:

• Modify /api/calculate POST route to do query MongoDB
  • Call getEgridRecordByKey() with the appropriate year and location parameters from the inputData
  • Call getAvertRecordByKey() with the appropriate year, location, and powerPlantClass from the inputData
• Add the variables in the resulting records to the FormulaParser using addVariable()

Additional Information

[ryanhu021]

Keep in mind EgridLocation and AvertLocation will be separate enums once #69 gets merged - need to figure out how this will work