File management, finishing patents quiz, more

Added preview folder to .gitignore. Added new images for the "beatles"
quiz. Added "patents" quiz. Changed the default validity of a choice to
false. Choices in a question's choice array can now just be strings
instead of objects. Questions now support an image. Reduced size of the
question size button. Began testing auto-detection of promo image in
the Facebook share dialog. Added question sub-text field for smaller
text to appear below the main question text.