Feature-complete API v2 model layer refactor

DONE: Remove CoreData
DONE: Replace CoreData models with JSONModel models
DONE: Refactor ViewController logic to match API v2 workflow
DONE: Replace Civic API v1 -> v2

TODO: Test partisan party picker w/ real data
TODO: Test election picker w/ real data
TODO: Fix Election.electionDay NSDate not parsing
TODO: Tests