JS refactor - sentence rendering, creating, updating working

I rewrote the JS to use the new position values, and in the process started to refactored it into a more OO structure with a Sentence class. Next step is to move the loose functions into a View module and a Story class, as well as continue to refactor Sentence methods.

I changed the DOM structure of the story view to reduce the number of unnecessary DIVs, styling might need to be changed to match. Also, new columns are being appended as a whole (with blank sentences) rather than piece by piece, I figured we can dynamically show/hide part of it if we want.

Performance is starting to be a concern with larger number of sentences.