Make letters into buttons that can be tapped to solve the puzzle.

SoK project by Sayan Biswas <techsayan01@gmail.com> with improvements.
Make 2 player score dialog invisible rather than opacity 0 so it doesn't
 prevent letter clicks.
Make each letter a button.
Add new LetterButton component to style all letters the same.
Change anagram to a QStringList so each letter gets it's own entry in
 the model.
Add userAnswer to keep track of which letters are in the answer area.

TODO: Check for puzzle solved.
Animate letter move?
Add chalk font to LetterButton