move Tab toggle button creation to registry

Add toggle property to Tab storing each tabs toggle button.
This way we are able to mark them as active when opening and
deactivating them again upon closing of a tab.

TabRegistry module now does create toggle buttons in
TabRegistry#createToggleFor.
Code was unnecessarily split up in two modules. Now the complete button
is handed over to the Tab for it to act upon it.

Remove unused method TabRegistry#open.

Change console.log to console.debug to less spam console output.
Mark active Tab toggles with upward triangle
move controlbar SCSS vars
Merge pull request #198 from line-o/active-tab-button

Active tab button
Set font-family of numbers to Monospace
decrease log spam
render time control items as an unordered list
improve readability of controls module
fix whitespace in timeline module
fix moderator

Register players using the src attribute of the iframe, again.
Remove log spam.
fix initially visible tabs

Refactor `TabRegistry.add` to expect a second parameter visible.
When true it will open the tab that is being added.

Refactor app module to add the second parameter accordingly.

Refactor modules with tabs to not set the active attribute directly.

* downloads
* info
* share
cleanup chapter module
Render a container for chapter-info in progressbar

A static solution for applying CSS.
Needs to be refactored:
So far, the active Chapter, which should be displayed above the
progress bar, is unreachable outside the chapter module.
The data of the current chapter should be stored in a central place.
Responsive layout for progress bar and its info items

The chapter title as well as the duration info is displayed above the
progress bar and will adapt to different screen solutions.
Set color and background color for chapter badge
fix character encoding issue in _progressbar.scss
WIP set current chapter title and badge
fix tab layout by resetting base font size

Flex box rules…. in a way.