Persist high scores using NSUserDefaults

CardGameViewController
 - Updating high scores whenever a game is completed (triggered by clicking of redeal button).
 - Score displayed in Red when negative and black when positive

Constants
 - Played around with several ways to declare constants in central file

FormatCardContent
 - Initiated move of formatting card content code to separate class for reuse.
Eliminated warning of avoid property getters with side effects: Changed   [NSUserDefaults standardUserDefaults].synchronize; -->   [[NSUserDefaults standardUserDefaults] synchronize];
Implemented  - Highlight highest score, least duration, latest play
Merge branch 'feature/High_Scores' into develop