New function: Validate Username
- added a function to validate that a user_identification string (format word-word-word) passed validation tests, including:
- when split at '-', number of words = settings.DICE_ROLLS
- all words in list in settings.word_list
User Landing - > CBV to FBV
- redefined 'landing' view as a function-based view (vs class-based view) to allow for easier integration of username validation/lookup functions; .validate_username called from within user_landing_view() function.
- added options to template to create a new codephrase or re-attempt login.