Responsify cyoa

Heya apps team! This is what we did over at the Trib to make the CYOA responsive. It's a pretty major change (the JS now generates slightly different HTML) so I wouldn't expect you to want to merge it but I thought you might be interested in seeing it anyway. 

Thanks again for talking us through using it last week! Please forgive any breaches of Git etiquette and let's keep up the inter-newsroom communication :dancer: 

Major points of interest:
- controls now all LI elements surrounded by a single UL, for ease generation/placement/manipulation
- only images, no background images, for responsive ease 
- paragraphs placed absolutely
- controls only at bottom, for mobile-friendliness
- a few options for how the controls appear
- a wrapper and some CSS style stuff