rewrite tab creation

Each tab is an instance of the new Tab-module. The share, downloads and
info tabs were rewritten to use it.
They are all added to the tab registry in each player.

Known Issues: The chapter tab is disabled until it is rewritten as well.
rewrite chapter tab

The chapter tab is an instance of the Tab-module as well. It is added
to the tab-registry.
Each chapter tab gets a reference to the update function to enable
highlighting of the currently played chapter.

TODO:  There is a need for a global update hook that can be listened to
by each tab.
Set config.rb to CSS output style with line-comments
Readme-update: Correct path to build podlove-webplayer.js
Rearrange markup for audio title area

- create wrapper for title and subtitle (h2 and h3)
- refactor calls for rendering the HTML for title area
- add some comments
Style title area with playbutton on the right

- pull playbutton .bigplay to the right with floating right
- add margin-right to subtitle to avoid covering the playbutton
rename class 'podlovewebplayer_controlbox' to 'tab'
update package.json
fix chapterTab name
refactor controls module

Controls constructor requires the player it is associated with as its
parameter.
Controls#createTimeControls requires an instance of the tab, the
chapterTab object.
Add getCombinedCallback utility function. It combines the standard
click handler with the specific given one.
add show property to configuration object of example players
disable line comments in built CSS by default

The current CSS output was added as well.
player module overhaul

Render show title with link to show main page when present.
Use playerType where applicable in main method.
Put all utility functions to the end of the module.