added gem Slim; rewrited Card views for Slim
rewrited Deck views for Slim
rewrited Index views for Slim
rewrited Layouts views for Slim
rewrited Users views for Slim
added metod Correct, Incorrect answers.
added metod calculation_time_to_update
added migration
fixed bug to Card model
fixed bug - icluded textarea instead input field
added unit test for Card model
fixed bugs to views, style scss:
renamed columns to Card table into DB
added unit tests for Card model
rewrited spec fo Card model
fixed bugs to Card model spec
fixed syntax to card spec
replaced all the inclusions to card spec: describe -> context
renamed def correct, incorrect answer