Initialize Core Data in the project

[eshajoshi]

Core Data Tutorials:

https://blog.bobthedeveloper.io/beginners-guide-to-core-data-in-swift-3-85292ef4edd https://www.raywenderlich.com/173972/getting-started-with-core-data-tutorial-2

[eshajoshi]

TODOs:

1. Create Core Data model
2. Create CoreDataController which:
   • Initialize the managed object model
   • Create the persistent store coordinator (which provides reference to the managed object context)
   • Implement the function for saving core data changes to the managed object context
3. Create protocol called "NetworkResponseHandleable" which defines functions for handling the JSON returned back from network calls to GoogleSheets APIs
4. Implement functions of NetworkResponseHandleable in CoreDataController file
   • Takes the JSON and creates object entities (calls protocol functions - step #5) on a background context in the persistent container
   • Saves changes to background context
5. Create functions for each entity that converts JSON to entities.... tbd in another comment