add popcorn.js
patch popcorn HTMLYouTubeVideoElement to allow popcorn#play to work
Enable skipping to time/slide
Remove stop attribute from Sequence
Enable editing of sequences for an given presentation
refactor: move decoding logic from IndexRoute to Presentation and Sequence models. Add encoding logic
Remove start time from presentation URLs. Popcorn-video is passed in the start time
Enable creation of new Presentations. Validate YT and SlideShare URLs