Merge pull request #2 from znagler/decks_and_cards

Decks and cards
added logic to user controller to only add a user to the db if they haven't been added yet
modified user create action in user controller
added quizlet_modified_time column to decks table
refactored create action for decks controller into helper methods in decks_helper
Change deck table and helper methods to create
deck objects to store an array of json objects
into a cards column in the deck table