refactor chapters to player module

Almost a rewrite of the chapter update logic. The chapter module knows
its state like the currentChapter and all available chapters in the
playing media file.
The chapter control buttons are working now. Although the example files
are too small/short to show this. Try with a longer media file.
Annoying autoplay is disabled for now, too.

TODOS: fix buffering in chrome, fix issues with ultra-short chapters,
create debug/log modules, separate module logic from rendering
enable tabs to be open on player init

currently implemented for the chapters tab only