Chapter hot fix

- Delete rendering of an external link next to the chapter name
- Delete unused debug log
- Comment-out chapter image column and delete its styles
(we’ll need it later for ‘unfold chapter summary’ feature and will
rename it then)
- Delete styling of chapter image column
- Add behavior of active and inactive chapter duration color
WIP re-enable video playback
re-enable video playback

* remove old mediaelement.js styles since we only use its API
* add _video.scss for styling the current video element
* rename `.podlovewebplayer_top` to `.video-pane`
* refactor event play button creation and event listeners in app module
* reuse play button for video playback

fixes https://trello.com/c/Bd0eeOgd/78-fix-video-player
add poster image to video example
Merge pull request #202 from podlove/fix-video

Fix video
use registered bower package for podlove font