Day 1 Hangman implementation -

implemented:
- checkLetter (checks if letter is in word)
- setUpWord (initializes the word, with inputted word)
- keyboard, automatically checks letter if a char is inputted. does
nothing for non-chars and converts uppercase to lowercase.
- settings, with UserDefaults and registerDefaults
- alphabet, with green, red and black letters for correct, wrong and
unguessed letters
various