1. add support for external site as a slide
2. move url shortener to own file
Fix slide-image/slide-iframe
1. Turn Playback into Sequences.
2. Extract Sequences from Presentation. Use sequences outlet in routes.
3. Do controller dependency injections into controllers via needs.
4. MediaController: tracks time, determines videoMode, controls animation
5. DeckController: tracks slide numbers, determines siteMode and site
6. fix dist index.html